DOC: also redirect old whatsnew url
The whatsnew was already splitted longer time ago, but I think we can also add a redirect for the main release page.
cc @TomAugspurger @datapythonista  That makes sense. We just need to add `release,whatsnew/index` to a new section in `doc/redirects.csv`. Ah, yes, that one as well. Will add. leave it for a beginner, surely someone if happy to take care of this :) Too late, and I am doing this because we want to release. oh, I thought this was a ticket, not a PR, was commenting from the phone :) When are you planning to release? Will try to work on the redirects for the API today.

Are we finally happy with `api/generated/`, or should I move them somewhere else?

Also, I think it'd be great to have #24890 in 0.24, do you mind taking a look? # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24906?src=pr&el=h1) Report
> Merging [#24906](https://codecov.io/gh/pandas-dev/pandas/pull/24906?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/94d989e4ae682bbd39f5599ef1d1f455bea0c3fd?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24906/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24906?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24906   +/-   ##
=======================================
  Coverage   92.39%   92.39%           
=======================================
  Files         166      166           
  Lines       52413    52413           
=======================================
  Hits        48425    48425           
  Misses       3988     3988
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.81% <ø> (ø)` | :arrow_up: |
| #single | `42.89% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24906?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24906?src=pr&el=footer). Last update [94d989e...20b0188](https://codecov.io/gh/pandas-dev/pandas/pull/24906?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24906?src=pr&el=h1) Report
> Merging [#24906](https://codecov.io/gh/pandas-dev/pandas/pull/24906?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/94d989e4ae682bbd39f5599ef1d1f455bea0c3fd?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24906/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24906?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24906   +/-   ##
=======================================
  Coverage   92.39%   92.39%           
=======================================
  Files         166      166           
  Lines       52413    52413           
=======================================
  Hits        48425    48425           
  Misses       3988     3988
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.81% <ø> (ø)` | :arrow_up: |
| #single | `42.89% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24906?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24906?src=pr&el=footer). Last update [94d989e...20b0188](https://codecov.io/gh/pandas-dev/pandas/pull/24906?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
