Change ReactiveCaching::LowUrgencyWorker to sticky

What does this MR do and why?

Change ReactiveCaching::LowUrgencyWorker to sticky

Changes the ReactiveCaching::LowUrgencyWorker to sticky data_consistency to move queries to replicas.

This worker runs a lot of queries without partition pruning against the CI primary as part of Security::MergeRequestSecurityReportGenerationService, contributing to 2026-03-16: Database lock contention causing sl... (gitlab-com/gl-infra/production#21562)

Moving the work to a replica should distribute the load.

References

gitlab-com/gl-infra/production#21562

How to set up and validate locally

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