Add Automatic Log Cleanup

Unless I'm missing this somewhere, there doesn't seem to be any mechanism for cleaning up old queue logs.
On queues that run frequently, this would result in the database table swelling in size over time.

Ideally, there would be a cron job that would periodically clean up completed or failed log entries.
This should be configurable per job type, based on time (i.e. keep logs for x days) or a limit (i.e. keep the last n log entries).