Support log4j format for timestamps (comma-milliseconds)

[mtojek]

The Go method time.ParseDuration only supports strings with "dot-milliseconds" format:
2006-01-02 15:04:05.000 (dot)

There were few inquiries already about support for log4j format:
2006-01-02 15:04:05,000 (comma)
e.g. https://discuss.elastic.co/t/using-timestamp-processor-fails/228348/2:

or "colon-milliseconds":
03.12.19 17:47:38:402 (colon)
#15012

The issue in Go project seems to be open for a longer time (golang/go#6189), I even spotted @sayden linking a similar issue. I think it would valuable for Beats to support this format out-of-the-box.

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[botelastic]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.