Make the ElasticIndexerWorker idempotent

Part of #178 (closed)

The ElasticIndexerWorker processed 100k "duplicate" jobs the past 7 days, and spent 3 hours on that. Duplicate jobs are jobs that get scheduled when there is already a job in the queue for the same worker with the same arguments.

If the job was (marked as) idempotent, we would be able to deduplicate those jobs when they get scheduled.

This worker will updates or deletes the document in elasticsearch for a record in the database. And possibly schedule an indexing of the repository. I think this worker is already idempotent and could be deduplicated, but we'd have to double check that with groupglobal search.