conf: parser: improve mongodb parser (#390)

- Fix field naming (context<->component)
- Add an optional "ms" field that will be the Microseconds the query took to execute (won't be there is it's not a COMMAND)

conf/parsers.conf

@@ -65,7 +65,7 @@
 [PARSER]
  Name mongodb
  Format regex
- Regex ^(?<time>[^ ]*)\s+(?<severity>\w)\s+(?<context>[^ ]+)\s+\[(?<connection>[^\]]+)]\s+(?<message>.*)$
+ Regex ^(?<time>[^ ]*)\s+(?<severity>\w)\s+(?<component>[^ ]+)\s+\[(?<context>[^\]]+)]\s+(?<message>.*?) *(?<ms>(\d+))?(:?ms)?$
  Time_Format %Y-%m-%dT%H:%M:%S.%L
  Time_Keep On
  Time_Key time