Fast track save code now requests

Currently, save code now requests may require a few hours to complete, sometimes more.

We want to reduce this waiting time to a few minutes (the average time we observed when the global ingestion process was paused a few months ago was a handful of seconds).

To this end, save code now request should be handled by a dedicated ingestion queue.

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Migrated from T3084 (view on Phabricator)