Give each elasticsearch worker its own sidekiq queue

What does this MR do?

Removes the elasticsearch queue, introducing two dedicated sidekiq queues instead - one per worker

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

The two workers are quite different in terms of resource usage, so we need to be able to throttle / control them separately. Otherwise, a large git push could delay issue search from being updated, among other sins.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Closes #2108 (closed)

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