**Describe the bug**

When retain in forwards is not set.
```
bridge.mqtt.emqx.forwards.1.remote_topic=fwd/topic1
bridge.mqtt.emqx.forwards.1.local_topic=topic1
```

No forwards information are printed when NanoMQ started.

```
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3281  print_bridge_conf: bridge.mqtt.emqx.qcongestion_control:        1
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3283  print_bridge_conf: bridge.mqtt.emqx.quic_0rtt:                  true
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3287  print_bridge_conf: bridge.mqtt.emqx.tls.enable:                 false
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3295  print_bridge_conf: bridge.mqtt.emqx.forwards:
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3307  print_bridge_conf: bridge.mqtt.emqx.subscription:
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3310  print_bridge_conf: 	[1] remote topic:        jaylin/1
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3313  print_bridge_conf: 	[1] local topic:        jaylin/2
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3316  print_bridge_conf: 	[1] qos:          1
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3318  print_bridge_conf: 	[1] rap:          1
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3320  print_bridge_conf: 	[1] rh:           1
```

Meanwhile some leaks found.
```
=================================================================
==196888==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 11 byte(s) in 1 object(s) allocated from:
    #0 0x7fc8c10d8cc7 in calloc (/lib64/libasan.so.8+0xd8cc7) (BuildId: 542ad02088f38edfdba9d4bfa465b2299f512d3e)
    #1 0x7d5221 in strtrim_head_tail /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:108
    #2 0x7d60bd in get_conf_value /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:275
    #3 0x7e3741 in conf_bridge_node_parse_forwards /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:2622
    #4 0x7e7582 in conf_bridge_node_parse_with_name /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3016
    #5 0x7e7ab2 in conf_bridge_content_parse /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3057
    #6 0x7e8072 in conf_bridge_parse /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3072
    #7 0x7d97e6 in conf_parse /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:635
    #8 0x737c94 in broker_start /home/wangha/Documents/nanomq/nanomq/apps/broker.c:1775
    #9 0x72cac0 in main /home/wangha/Documents/nanomq/nanomq/nanomq.c:142
    #10 0x7fc8bfe49b89 in __libc_start_call_main (/lib64/libc.so.6+0x27b89) (BuildId: f888be5f5e7d58e04cabb8c675c7ab94e77dd68c)
    #11 0x7fc8bfe49c4a in __libc_start_main_alias_2 (/lib64/libc.so.6+0x27c4a) (BuildId: f888be5f5e7d58e04cabb8c675c7ab94e77dd68c)
    #12 0x6e8e84 in _start (/home/wangha/Documents/nanomq/build/nanomq/nanomq+0x6e8e84) (BuildId: f53c8027906b2f56e12856101314e9ed69ceebea)

Direct leak of 7 byte(s) in 1 object(s) allocated from:
    #0 0x7fc8c10d8cc7 in calloc (/lib64/libasan.so.8+0xd8cc7) (BuildId: 542ad02088f38edfdba9d4bfa465b2299f512d3e)
    #1 0x7d5221 in strtrim_head_tail /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:108
    #2 0x7d60bd in get_conf_value /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:275
    #3 0x7e3822 in conf_bridge_node_parse_forwards /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:2632
    #4 0x7e7582 in conf_bridge_node_parse_with_name /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3016
    #5 0x7e7ab2 in conf_bridge_content_parse /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3057
    #6 0x7e8072 in conf_bridge_parse /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3072
    #7 0x7d97e6 in conf_parse /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:635
    #8 0x737c94 in broker_start /home/wangha/Documents/nanomq/nanomq/apps/broker.c:1775
    #9 0x72cac0 in main /home/wangha/Documents/nanomq/nanomq/nanomq.c:142
    #10 0x7fc8bfe49b89 in __libc_start_call_main (/lib64/libc.so.6+0x27b89) (BuildId: f888be5f5e7d58e04cabb8c675c7ab94e77dd68c)
    #11 0x7fc8bfe49c4a in __libc_start_main_alias_2 (/lib64/libc.so.6+0x27c4a) (BuildId: f888be5f5e7d58e04cabb8c675c7ab94e77dd68c)
    #12 0x6e8e84 in _start (/home/wangha/Documents/nanomq/build/nanomq/nanomq+0x6e8e84) (BuildId: f53c8027906b2f56e12856101314e9ed69ceebea)

SUMMARY: AddressSanitizer: 18 byte(s) leaked in 2 allocation(s).
```

Bridge forwards will not take effect until retain is set in old_conf.
This is a GitHub Issue
repo:nanomq
owner:emqx
Title : Bridge forwards will not take effect until retain is set in old_conf.
Issue date:

--- start body ---
**Describe the bug**

When retain in forwards is not set.
```
bridge.mqtt.emqx.forwards.1.remote_topic=fwd/topic1
bridge.mqtt.emqx.forwards.1.local_topic=topic1
```

No forwards information are printed when NanoMQ started.

```
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3281  print_bridge_conf: bridge.mqtt.emqx.qcongestion_control:        1
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3283  print_bridge_conf: bridge.mqtt.emqx.quic_0rtt:                  true
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3287  print_bridge_conf: bridge.mqtt.emqx.tls.enable:                 false
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3295  print_bridge_conf: bridge.mqtt.emqx.forwards:
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3307  print_bridge_conf: bridge.mqtt.emqx.subscription:
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3310  print_bridge_conf: 	[1] remote topic:        jaylin/1
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3313  print_bridge_conf: 	[1] local topic:        jaylin/2
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3316  print_bridge_conf: 	[1] qos:          1
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3318  print_bridge_conf: 	[1] rap:          1
2024-05-28 23:50:50 [196650] INFO  /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3320  print_bridge_conf: 	[1] rh:           1
```

Meanwhile some leaks found.
```
=================================================================
==196888==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 11 byte(s) in 1 object(s) allocated from:
    #0 0x7fc8c10d8cc7 in calloc (/lib64/libasan.so.8+0xd8cc7) (BuildId: 542ad02088f38edfdba9d4bfa465b2299f512d3e)
    #1 0x7d5221 in strtrim_head_tail /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:108
    #2 0x7d60bd in get_conf_value /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:275
    #3 0x7e3741 in conf_bridge_node_parse_forwards /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:2622
    #4 0x7e7582 in conf_bridge_node_parse_with_name /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3016
    #5 0x7e7ab2 in conf_bridge_content_parse /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3057
    #6 0x7e8072 in conf_bridge_parse /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3072
    #7 0x7d97e6 in conf_parse /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:635
    #8 0x737c94 in broker_start /home/wangha/Documents/nanomq/nanomq/apps/broker.c:1775
    #9 0x72cac0 in main /home/wangha/Documents/nanomq/nanomq/nanomq.c:142
    #10 0x7fc8bfe49b89 in __libc_start_call_main (/lib64/libc.so.6+0x27b89) (BuildId: f888be5f5e7d58e04cabb8c675c7ab94e77dd68c)
    #11 0x7fc8bfe49c4a in __libc_start_main_alias_2 (/lib64/libc.so.6+0x27c4a) (BuildId: f888be5f5e7d58e04cabb8c675c7ab94e77dd68c)
    #12 0x6e8e84 in _start (/home/wangha/Documents/nanomq/build/nanomq/nanomq+0x6e8e84) (BuildId: f53c8027906b2f56e12856101314e9ed69ceebea)

Direct leak of 7 byte(s) in 1 object(s) allocated from:
    #0 0x7fc8c10d8cc7 in calloc (/lib64/libasan.so.8+0xd8cc7) (BuildId: 542ad02088f38edfdba9d4bfa465b2299f512d3e)
    #1 0x7d5221 in strtrim_head_tail /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:108
    #2 0x7d60bd in get_conf_value /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:275
    #3 0x7e3822 in conf_bridge_node_parse_forwards /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:2632
    #4 0x7e7582 in conf_bridge_node_parse_with_name /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3016
    #5 0x7e7ab2 in conf_bridge_content_parse /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3057
    #6 0x7e8072 in conf_bridge_parse /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:3072
    #7 0x7d97e6 in conf_parse /home/wangha/Documents/nanomq/nng/src/supplemental/nanolib/conf.c:635
    #8 0x737c94 in broker_start /home/wangha/Documents/nanomq/nanomq/apps/broker.c:1775
    #9 0x72cac0 in main /home/wangha/Documents/nanomq/nanomq/nanomq.c:142
    #10 0x7fc8bfe49b89 in __libc_start_call_main (/lib64/libc.so.6+0x27b89) (BuildId: f888be5f5e7d58e04cabb8c675c7ab94e77dd68c)
    #11 0x7fc8bfe49c4a in __libc_start_main_alias_2 (/lib64/libc.so.6+0x27c4a) (BuildId: f888be5f5e7d58e04cabb8c675c7ab94e77dd68c)
    #12 0x6e8e84 in _start (/home/wangha/Documents/nanomq/build/nanomq/nanomq+0x6e8e84) (BuildId: f53c8027906b2f56e12856101314e9ed69ceebea)

SUMMARY: AddressSanitizer: 18 byte(s) leaked in 2 allocation(s).
```

--- end body ---
