Fix timeout errors when loading expired job artifacts

What does this MR do?

Related to #281688 (closed)

Ci::DestroyExpiredJobArtifactsService#destroy_job_artifacts_batch tries to load batches of expired artifacts but it fails with statement timeout: https://log.gprd.gitlab.net/goto/a8d3af0ba5d30a6ac56bdc0593a02565. As we can see from the json.duration_s column, this timeout doesn't happen right away, but after a good few executions, which means that it successfully removes the recently expired and unlocked artifacts, but it has to jump over a lot of locked ones to find more.

Query and execution plans before the change: https://explain.depesz.com/s/GOpw

New idea from EachBatch docs:

Select batches of expired artifacts and apply pipeline locked filtering to each batch. This is a simplified version:

Ci::JobArtifact.where('expired < ?', Time.current).each_batch(column: :expire_at) do |relation|
  destroy relation.unlocked.to_a
end

EachBatch queries:

• https://explain.depesz.com/s/0vWS
• https://explain.depesz.com/s/5eoc
• https://explain.depesz.com/s/nr5Q

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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