Settingize the job timeouts

Sentry Issues: ARKINDEX-BACKEND-DB, ARKINDEX-BACKEND-PK, ARKINDEX-BACKEND-D9

The default timeout for export jobs has been increased to 7200 seconds in #776 (closed), but it should also be increased for worker result deletion (and maybe also for element deletions). Instead of having those timeouts hardcoded, we can have a single job_timeout setting or a group of settings:

job_timeouts:
  export_corpus: 7200
  worker_results_delete: 3600
  element_trash: 3600

@babadie Should there be multiple settings or only one and should the defaults all be 7200 seconds or something else?