feat: Allow creating redis.action_cable.yml

What does this MR do?

feat: Allow creating redis.action_cable.yml

This is a second attempt at this change as the first one wasn't properly e2e-tested.

Used to migrate from the cluster specified in cable.yml, so cable.yml will point to the old cluster and redis.action_cable.yml will point to the new one. Eventually both should point to the new cluster and then we would not need the new file.

Related to gitlab-com/gl-infra/tenant-scale/tenant-services&41 (closed)

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