Optimize index_should_be_marked_as_orphaned_check with a single batch

Background

index_should_be_marked_as_orphaned_check runs on full records of zoekt_indices. This can put too much stress on the database. The second issue could be that in a single run, all zoekt_indices might not get processed and they will get re-enqueued after 10 minutes which will increase redundancy.

Proposal

Publish the event in the scheduling_service without any zoekt_indices_id. In the worker OrphanedIndexEventWorker add order(:id) and limit(1000) on the scope should_be_marked_as_orphaned to process just one batch.