Fix PauseControl sidekiq middleware

What does this MR do and why?

During the Zoekt incident gitlab-com/gl-infra/production#17266 (closed) we noticed that PauseControl Sidekiq middleware didn't pause all Zoekt indexing operations as we expected. After some debugging I've noticed that the client part of the middeware receives worker_class, but the server one receives worker instance, which caused this bug for the latter.

Because of this mismatch the second part wasn't working properly and was also returning strategy: :none.

The simplest way to test it is

Gitlab::SidekiqMiddleware::PauseControl::WorkersMap.strategy_for(worker: Zoekt::IndexerWorker.new)

On master it's:

[1] pry(main)> Gitlab::SidekiqMiddleware::PauseControl::WorkersMap.strategy_for(worker: Zoekt::IndexerWorker.new)
=> nil
[2] pry(main)> Gitlab::SidekiqMiddleware::PauseControl::WorkersMap.strategy_for(worker: Zoekt::IndexerWorker)
=> :zoekt

And on this branch:

[1] pry(main)> Gitlab::SidekiqMiddleware::PauseControl::WorkersMap.strategy_for(worker: Zoekt::IndexerWorker.new)
=> :zoekt
[2] pry(main)> Gitlab::SidekiqMiddleware::PauseControl::WorkersMap.strategy_for(worker: Zoekt::IndexerWorker)
=> :zoekt

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Before	After

How to set up and validate locally

1. Set up Zoekt
2. Check out master

   git checkout master

3. Restart Sidekiq

   gdk restart rails-background-jobs

4. Truncate zoekt index

   Gitlab::Search::Zoekt::Client.instance.truncate

5. Ensure that you don't have files in $GDK_DIR/zoekt-data/development/index
6. Restart rails console and perform these commands (in that order). This is specifically to schedule the job in the future before we pause indexing

   Zoekt::IndexerWorker.perform_in(65, 7, { "foo" => Time.now.to_i })
   ::Feature.enable(:zoekt_pause_indexing)

7. Monitor $GDK_DIR/zoekt-data/development/index and tail -f log/sidekiq.log | fgrep Zoekt
8. In 65 seconds you should see that the job has been executed and index files in $GDK_DIR/zoekt-data/development/index appeared
9. Checkout this branch fix-pause-control-middleware
10. Restart Sidekiq

    gdk restart rails-background-jobs

11. Truncate zoekt index, disable the FF, and clear the ZSET

    ::Feature.disable(:zoekt_pause_indexing)
    PauseControl::ResumeWorker.new.perform
    # Wait a few seconds so that existing jobs complete
    Gitlab::Search::Zoekt::Client.instance.truncate

12. Ensure that you don't have files in $GDK_DIR/zoekt-data/development/index
13. Perform these commands (in that order). This is specifically to schedule the job in the future before we pause indexing

    Zoekt::IndexerWorker.perform_in(65, 7, { "foo" => Time.now.to_i })
    ::Feature.enable(:zoekt_pause_indexing)

14. Monitor $GDK_DIR/zoekt-data/development/index and tail -f log/sidekiq.log | fgrep Zoekt
15. Wait for log records with "job_status":"paused"
16. In 65 seconds you should not see that the job has been executed and the $GDK_DIR/zoekt-data/development/index directory should be empty
17. You can also check that this commands returns 1

    Gitlab::SidekiqMiddleware::PauseControl::PauseControlService.queue_size('Zoekt::IndexerWorker')

18. Do not forget to unpause indexing

    ::Feature.disable(:zoekt_pause_indexing)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.