Discovery for integrating unified backup and restore (object storage) into Cells management

Summary

The unified backup and restore team created an MVC for backing up object storage in GCP. This issue will be to take that MVC and figure out how best to integrate this into the way we manage cells.

Goals

• Create an updated blueprint to explore Unified Backup and Cells integration gitlab-com/content-sites/handbook!7946 (merged)
• Set ourselves up for path forward for other backup components like the cloudsql and gitaly disk
• Ensure we have a plan for restores using Unified Backup

References:

• DR blueprint for Cells gitlab-org/gitlab!146189 (merged)
• Dedicated recovery guide https://gitlab-com.gitlab.io/gl-infra/gitlab-dedicated/team/runbooks/regional-failure-recovery.html
• Dedicated guide for restoring from backups https://gitlab.com/gitlab-com/gl-infra/gitlab-dedicated/team/-/blob/main/runbooks/restore-from-backups.md#full-system-restore
• Benchmark epic for validating RTO/RPO on Dedicated https://gitlab.com/groups/gitlab-com/gl-infra/gitlab-dedicated/-/epics/292
• Geo failover runbook for Dedicated https://gitlab-com.gitlab.io/gl-infra/gitlab-dedicated/team/runbooks/geo.html#failover
• Geo failover firedrills for Dedicated https://gitlab-com.gitlab.io/gl-infra/gitlab-dedicated/team/runbooks/rto-rpo-drill.html
• Cells DR proposal using backups https://docs.google.com/document/d/1N6ow0r2RbtJH5H9L_ND2ErpbwQEovn_qO8A88Yv3eLU/edit#heading=h.rm2ssz9b6jd1
• Dedicated backup blueprint https://gitlab.com/gitlab-com/gl-infra/gitlab-dedicated/team/-/blob/main/architecture/blueprints/backups.md
• Cloud-based Backups MVC (gitlab-org&14322 - closed)