Adds syslog sink support

[DerekHeldtWerle]

Adds support for a dedicated syslog server sink versus one listening at an http endpoint. Code draws heavy inspiration from the httpSink, with the minimal necessary changes to get it to work with a syslog server.

Signed-off-by: Derek Heldt-Werle derek.heldt-werle@viasat.com

[colml]

Good to see this @DerekHeldtWerle.

I wanted to integrate to Fluent Bit which has support for syslog input using in_syslog. However some log events cannot be parsed as syslog.Write() seems to add its own non-RFC5424 headers on top of the existing RFC5424 header written by EventData.WriteRFC5424().

For example if two events are sent together by syslogsink:

<syslog.Write() header> <rfc5424 header> <msg>
<rfc5424 header> <msg>

The second event will be parsed successfully but the first is not due to the double non rfc5424 header. It's possible to update the syslog parsing regex in Fluent Bit parsers to handle this issue, but might be worth investigating if additional header can be skipped.