title: log key is not parsed by fluent-bit (both Docker containerized)
body: <p>My regex parser doesn't seem to work.
  I'm guessing it has something to do with the logs coming from Docker and not being escaped.
  But I can't get it to work even if I include the Docker parser first.</p>
  
  <p>I've checked it in rubular: <a href="https://rubular.com/r/l6LayuI7MQWIUL" rel="nofollow noreferrer">https://rubular.com/r/l6LayuI7MQWIUL</a></p>
  
  <p><strong>fluent-bit.conf</strong></p>
  
  <pre><code>[SERVICE]
      Flush        5
      Daemon       Off
      Log_Level    debug
      Parsers_File parsers.conf
  
  [INPUT]
      Name         forward
      Listen       0.0.0.0
      Port         24224
  
  [FILTER]
      Name         grep
      Match        *
      Regex        log ^.*{.*}$
  
  [FILTER]
      Name         parser
      Match        *
      Key_Name     log
      Parser       springboot
  
  [OUTPUT]
      Name stdout
      Match *
  </code></pre>
  
  <p><strong>parsers.conf</strong></p>
  
  <pre><code>[PARSER]
      Name        springboot
      Format      regex
      Regex       (?&lt;time&gt;\d{4}-\d{1,2}-\d{1,2} \d{1,2}:\d{1,2}:\d{1,2}.\d{1,3}) (?&lt;level&gt;[^ ]*) (?&lt;number&gt;\d*) --- (?&lt;thread&gt;\[[^ ]*) (?&lt;logger&gt;[^ ]*) *: (?&lt;message&gt;[^ ].*)$
      Time_Key    time
      Time_Format %Y-%m-%d %H:%M:%S.%L
  
  [PARSER]
      Name         docker
      Format       json
      Time_Key     time
      Time_Format  %Y-%m-%dT%H:%M:%S.%L
      Time_Keep    On
      # Command      |  Decoder | Field | Optional Action
      # =============|==================|=================
      Decode_Field_As   escaped    log
  </code></pre>
  
  <p><strong>stout output</strong></p>
  
  <pre><code>[0] docker-container: [1584997354.000000000, {"log"=&gt;"2020-03-23 21:02:34.077 TRACE 1 --- [nio-8080-exec-1] org.zalando.logbook.Logbook              : {...}", "container_id"=&gt;"5a1251dcf9de3f0e2b8b7b0bce1d35d9c9285726b477606b6448c7ce9e818511", "container_name"=&gt;"/xxxx", "source"=&gt;"stdout"}]
  </code></pre>
  
  <p>Thanks</p>