Syslog Input Support for additional timestamp formats

[tellistone]

What?

Syslog supports various timestamps, like the well-known and currently supported RFC5424 (1985-04-12T23:20:50.52Z)

However where an unsupported format is hit, for example, BSD Format (RFC3164), it becomes necessary to use a GROK pattern in order to get to the timestamp.

The request is that we add explicit support by the syslog input for this, and other, timestamp formats. This might be managed via an option on the Input itself.

Why?

Customers report this being a pain point. Example: https://github.com/Graylog2/support/issues/149