Catch block in EmitBatchAsync() prevents fallback sinks from running

[nblumhardt]

Howdy! :-)

Serilog now supports failure listeners natively, which among other things, allows failed batches to be rerouted to an alternative sink:

https://nblumhardt.com/2024/10/fallback-logging/

Unfortunately, this doesn't quite work with the PostgreSQL sink, because exceptions are suppressed after invoking the failureCallback.

https://github.com/serilog-contrib/Serilog.Sinks.Postgresql.Alternative/blob/master/src/Serilog.Sinks.Postgresql.Alternative/Sinks/PostgreSQL/PostgreSQLSink.cs#L54

I'd suggest deprecating failureCallback, and changing the implementation to:

        catch (Exception ex)
        {
            this.sinkHelper.SinkOptions.FailureCallback?.Invoke(ex);
            throw;
        }

The Serilog infrastructure also handles SelfLog so this can be dropped.

Let me know if you'd like a PR along these lines. Cheers!