Geo: GA support for failover in multi-secondary configurations
## Context
From https://gitlab.com/groups/gitlab-org/-/epics/3574#note_740635830:
> Nick Nguyen `@nhxnguyen` · 13 hours ago
> `@fzimmer @vsizov @dbalexandre` I just noticed in https://docs.gitlab.com/ee/administration/geo/disaster_recovery/, at the top of the page, that we say DR is in alpha for multi-secondary configurations and to check this epic. I'm not sure I've seen any open issues for this. But I did see gitlab#4364 (closed). Is this just a matter of testing and documentation?
## Proposal
@dbalexandre's proposal from https://gitlab.com/groups/gitlab-org/-/epics/3574#note_740658309.
To remove the `alpha` designation for failover in multi-secondary configurations:
1. Test and revisit the documentation to ensure it's updated.
Further improvements for GitLab 14.5 and later:
1. We don't need to enable the Geo Primary role if the secondary site has been promoted with the new single command;
1. We can extend the new single command to accept a list of secondary PostgreSQL node IP's and applies the required changes with no manual interaction;
1. Validate the promotion of a secondary Geo site in multi-secondary configurations using our reference architectures;
1. Validate what happens with current data on other secondary sites. Do we need to re-synchronize everything?
1. Create a new command gitlab-ctl geo set-primary 1.2.3.4 to automate the steps mentioned here https://docs.gitlab.com/ee/administration/geo/disaster_recovery/#step-2-initiate-the-replication-process;
epic