Exit Criteria: * [x] Set-up * [x] An engineer who did not develop this feature can follow the documentation to set up a standby cluster * [x] All known bootstapping issues are either resolved or have acceptable workarounds. Fixes to known issues will not result in breaking changes (ex. require existing users to resync everything). * [x] Load balancing enabled and tested. https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/12857 * [x] Common admin operations are well-tested. Any problems are well-understood and have acceptable workarounds. * [x] Failover from multi-node primary to multi-node secondary using Patroni standby cluster * [x] Pause and resume replication * [x] Maintenance mode enabled/disabled * [x] GitLab version upgrade * [x] Performance test performed on an architecture using Patroni standby cluster on Geo secondary. No notable performance regressions. * [x] Collaborate with Quality to define a test plan for Patroni set-up steps and failover to secondary with standby cluster on various reference architectures. Necessary issues are created.