Shift DB load from Primary to Replicas Rapid Action | Goal 3: BuildHooksWorker queries read-replicas
### Goal 3: `BuildHooksWorker` queries read-replicas
The broader goal is to allow Sidekiq to use read replicas, so that read-only jobs don't put pressure on the primary postgres instance. However, in the scope of the rapid action, we focus on getting just the first worker, on the assumption that others should be relatively easy to migration once the pattern has been established.
https://gitlab.com/gitlab-org/gitlab/-/issues/322452
**Exit criteria** https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55881 has been rolled out **on Staging and Production** and any requisite infrastructure changes (eg: pgbouncer pools for Sidekiq to postgres read-replicas, are complete.
epic