fix EZP-23312: asynchronous publisher: old processes are filling up the ...

JIRA: https://jira.ez.no/browse/EZP-23312

introduces the --cleanup-loop option, which defaults to 43200 seconds (twice a day)
it's not immediately, it will be on next second, in the course of the run(). and it's a secondary, non-critical cleanup, make it abort seem excessive. even the main run() process, much more "important" than this, keeps retrying too. if anything, the main run() should decide/abort a DB fatal error, but that's not the scope of this fix.