Addition of pgaudit.log_rotation_size option

[Nd1002]

Good afternoon!
When using 'pgauditlogtofile', there was a need to rotate the file based on its size.
Adding log file rotation based on the size set in pgaudit.log_rotation_size. The unit of measurement is the same as in PostgreSQL's standard logging. pgaudit.log_rotation_size is only set by the user; otherwise, its functionality will be disabled.
This feature was tested in various scenarios, including with pgbench. When enabled, microseconds are added to the log file name (assuming the standard 'pgaudit-%Y-%m-%d_%H%M%S.log' template), changing it to 'pgaudit-%Y-%m-%d_%H%M%S-%ms.log', this is needed when pgaudit.log_rotation_size is set to a small value.

I would appreciate your corrections and suggestions!

[fmbiete]

Thank you for the contribution! I like the idea of having the option of doing a rotation by size.
Some thoughts:
The filename could be something like: <pgaudit.log_filename>[.N] where N is > 0
So, if I select rotate by day and rotate after 10GB, I would have

pgaudit-20240815.log <- this always the active
pgaudit-20240815.log.1 <- first rotation after 10GB
pgaudit-20240815.log.2 <- second rotation after 20GB
pgaudit-20240815.log.3 <- third rotation after 30GB

that would require some file rename