Change cron worker to queue sub-workers

What does this MR do and why?

The current approach with the click_house_ci_finished_builds_sync_worker (introduced in %16.5) doesn't allow for having multiple runners, even though it accepts arguments. In this MR, we're fixing this shortcoming by doing the following:

1. Add a new ClickHouse::CiFinishedBuildsSyncWorker class that will perform the same work as the previous cronjob worker
2. Change the existing ClickHouse::CiFinishedBuildsSyncCronWorker so it takes a total number of workers and dispatches the appropriate ClickHouse::CiFinishedBuildsSyncWorkers;
3. Add a version value to ClickHouse::CiFinishedBuildsSyncCronWorker so that it ignores jobs that were queued without a version, as we don't really mind discarding those.

I didn't feel it was necessary to go through the process specified in https://docs.gitlab.com/ee/development/sidekiq/compatibility_across_updates.html#changing-the-arguments-for-a-worker since we haven't released the original worker yet.

EE: true

Part of #421201 (closed)

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