Review test process and coverage for Postgres upgrades
This issue is to explore how to increase PG upgrades test coverage. Below are some areas that could be reviewed:
- Upgrade to the newer PG version
- Downgrade to the older PG version
- Replication and failover
- Zero-data loss Recovery - if leader fails, would other nodes lost data
- Postgres configuration overrides
- Check all Patroni commands (switch over, recover, etc.)
- Check the docs for improvements
Additionally explore running pipelines for PG upgrades periodically using https://gitlab.com/gitlab-org/quality/postgres-upgrade-testing and add further scenarios.