Draft: [Do not merge!] Spike batch updates on job artifacts belonging to a pipeline

What does this MR do and why?

This is a spike to assess a way to improve the update queries in the existing Ci::UnlockArtifactsService.

The update_job_artifacts query in Ci::UnlockArtifactsService was identified to have the potential to generate unbounded WAL.

This MR describes a way to break the workload into smaller batch of updates on a single pipeline that can then be rate-controlled.

Related: #379089 (closed)

To illustrate this conceptually, here is an overview of the desired process:

The existing behaviour is shown in black, where every time Ci::UnlockArtifactsService is called, it queries for all pipeline IDs that need to be unlocked, then it unlocks the job & pipeline artifacts in all of these pipelien IDs.

This MR introduces the feature flagged part in green, where Ci::UnlockArtifactsService would enqueue the list of pipeline IDs into a database-backed queue Ci::UnlockPipelineRequest. A new worker Ci::UnlockPipelineAndArtifactsWorker will pick a single pipeline off the queue in order to unlock the pipeline and its associated artifacts. This worker uses LimitedCapacity::Worker to give us the ability to control the rate at which the pipelines are unlocked.

With this in place, we can then resume fixing unlocking pipelines in failed & blocked states. With the queue in place, the fix to these issues can directly insert the pipeline IDs into Ci::UnlockPipelineRequest and reuse the same unlocking process for the artifacts (shown in blue).

Screenshots or screen recordings

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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