Adds scheduled import jobs to the stuck import jobs detection worker.

Merged Tiago Botelho requested to merge mark-scheduled-mirrors-as-stuck into master

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?

What are the relevant issue numbers?

Edited by Douwe Maan