title: how to promtail parse json to label and timestamp
body: <p>I have a probleam to parse a json log with promtail, please, can somebody help me please. I try many configurantions, but don't parse the timestamp or other labels.</p>
  
  <p><strong>log entry:</strong></p>
  
  <pre><code>{timestamp=2019-10-25T15:25:41.041-03, level=WARN, thread=http-nio-0.0.0.0-8080-exec-2, mdc={handler=MediaController, ctxCli=127.0.0.1, ctxId=FdD3FVqBAb0}, logger=br.com.brainyit.cdn.vbox.
  controller.MediaController, message=[http://localhost:8080/media/sdf],c[500],t[4],l[null], context=default}
  </code></pre>
  
  <p><strong>promtail-config.yml</strong></p>
  
  <pre><code>server:
    http_listen_port: 9080
    grpc_listen_port: 0
  
  positions:
    filename: /tmp/positions.yaml
  
  clients:
    - url: http://localhost:3100/loki/api/v1/push
  
  scrape_configs:
  - job_name: vbox-main
    static_configs:
    - targets:
      - localhost
      labels:
        job: vbox
        appender: main
        __path__: /var/log/vbox/main.log        
  
    pipeline_stages:
    - json:
        expressions:
          timestamp: timestamp
          message: message
          context: context
          level: level
        timestamp:
          source: timestamp
          format: RFC3339Nano
        labels:
          context:
          level:
        output:
          source: message
  </code></pre>