Upgrade redis gem in gitlab-rails

This issue tracks the efforts to upgrade the redis gem for gitlab rails as part of epic &941.

Since the redis gem is used widely within the application, a major version bump should be performed carefully and mindful of breakages.

• Preliminary review of the v5 gem's feasibility and challenges are outlined in #2571 (closed)
• The workaround for the external dependency breakage is being explored in #2585 (closed)
• The resolution of breakages due to type strictness in the upgraded gem is being discussed in #2586 (closed)

Deployment

• In the redis-cluster-client, there are environment variables affecting start-up which we need to set before deployment. See #2571 (comment 1632753362).
  • gstg change: gitlab-com/gl-infra/k8s-workloads/gitlab-com!3345 (merged)
  • gprd change: gitlab-com/gl-infra/k8s-workloads/gitlab-com!3348 (merged)
• We would need to engage groupdelivery on how this can be safely rolled out. We may need an isolated deployment like sidekiq. For redis, cny would be useful since the webservices would use Redis actively and would surface some problems ahead of the main gprd deployment.