Update GitLab's Redis architecture

Why is this change being made?

With the completion of a few sharding/migration works, the architecture diagram needs to be updated.

• gitlab-com/gl-infra&857 (closed) (repository-cache)
• gitlab-com/gl-infra&823 (closed) (Redis Cluster for ratelimiting)
• gitlab-com/gl-infra&877 (closed) (db-load-balancing)

In this MR, I'm proposing the use of a matrix-table since there are 9 Redis instances and it is getting messy.

Validation of the relationships can be done against thanos.

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