Test GitLab Secrets Manager failover to Geo secondary and secondary domain
## Summary
Test GitLab Secrets Manager in a Geo failover scenario where the secondary site in on a secondary domain.
Update existing docs to better cover that scenario, if needed.
This is a follow-up to https://gitlab.com/gitlab-org/gitlab/-/work_items/571922+
that tested and documented a Geo failover scenario
where the DNS record of the primary domain are updated
to point to the secondary site.
## Scenario
Test the following failover scenario:
1. Generate recovery key for OpenBao. See https://gitlab.com/gitlab-org/gitlab/-/work_items/594034
1. Fail over to a secondary site – it's accessible through the secondary domain.
1. Reconfigure OpenBao's JWT auth on the secondary site. Use recovery key.
1. Check that GitLab Secrets Manager is fully functional on the secondary.
## Implementation plan
- [x] Test failover to secondary site with secondary domain.
- [x] Confirm that JWT authentication can be reconfigured as needed.
- [ ] Update [Geo disaster recovery](https://docs.gitlab.com/administration/geo/disaster_recovery/#step-4-optional-promote-the-openbao-ha-cluster) docs to cover the scenario.
- [ ] Update [admin docs](https://docs.gitlab.com/administration/secrets_manager/), and specifically the section introduced in https://gitlab.com/gitlab-org/gitlab/-/work_items/593460.
- [ ] Update OpenBao Chart docs if needed, and in particular the [Geo configuration](https://docs.gitlab.com/charts/charts/openbao/#geo-configuration) section.
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