Calculate indexing duration from queue to completion

Problem to solve

groupglobal search does not have a view for how long it takes git data indexing (think blobs, commits, wikis) to occur. As we add additional context to the index from those sources, we need to ensure indexing is happening quickly and efficiently. Currently, the indexing SLIs for repository data measures how long the indexing request takes but is missing the time waiting in the queue.

Proposal

ElasticCommitIndexerWorker and ElasticCommitIndexerWorker both have measurements for indexing time. Both workers have an options param. We should send into that options param the queue_timestamp which can determine when the record was queued and how long it took to be indexed.

This would give a more accurate value of how long it takes for indexing to complete from initiation time.