Add template chart cluster support for Registry Redis cache

This issue is meant to introduce redis.cache.cluster param which is needed as a pre-requisite of gitlab-com/gl-infra/k8s-workloads/gitlab-com!4641 (merged).

The background context is to point registry cache to use redis-cluster-registry instead of redis-registry-cache which in-turn requires upgrading of redis helm chart as currently redis.cache.cluster is not supported.

This is being done as a part of migration of redis-registry-cache to redis-cluster-registry

Related slack conversation: https://gitlab.slack.com/archives/C07U8G0LHEH/p1754398317658019

This issue further solves gitlab-com/gl-infra/k8s-workloads/gitlab-com!4641 (merged)