Keep original log message when using Syslog input

[strawgate]

Describe the enhancement:
When using the syslog input the original message is not stored in log.original. As processors run after the input parsing is completed you cannot use copy_field to get the original message back.

Describe a specific use case for the enhancement or feature:
Allow for reprocessing of syslogs in the future and allow for viewing the entire original log message.

[exekias]

related to #14708

[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.

[strawgate]

I think this is an open feature request