Adds scheduled import jobs to the stuck import jobs detection worker.
According to https://gitlab.com/gitlab-com/infrastructure/issues/2912#note_42272315 we can confirm that we do have
scheduled mirrors that don't have a worker anymore to finish their work.
The way we can fix this is by getting both scheduled and started jobs that have been enqueued for more than 15 hours.
Does this MR meet the acceptance criteria?
- Changelog entry added, if necessary
- Documentation created/updated
- API support added
- Tests added for this feature/bug
- Has been reviewed by UX
- Has been reviewed by Frontend
- Has been reviewed by Backend
- Has been reviewed by Database
- Conform by the merge request performance guides
- Conform by the style guides
- Squashed related commits together