DLB: Expose settings for dedicated Redis connection

Context

Related to Container Registry: DLB Phase 2 (&15998).

Task

To simplify the rollout, the Phase 1 of database load balancing relied on the existing Redis cache instance that we have available on .com. According to the plan, before expanding the coverage of DLB to additional API routes, we should switch to a new Redis cluster dedicated to load balancing.

We need to expose the configuration settings for this new instance in the registry config and its Distribution Helm chart. While the dedicated Redis load balancing instance is not available, we should fallback to the Redis cache instance.