Research spike: Adding support for PG14

Summary

• Research the work required to add PostgreSQL 14 as opt-in
• Create issues to capture the work that needs to be done
• Link the issues to &9065 (closed)

Note the intent is to ship PostgreSQL 14 as opt-in in GitLab 16. (see https://about.gitlab.com/handbook/engineering/development/enablement/data_stores/database/postgresql-upgrade-cadence.html) But that is best case scenario, where we only need to swap in the version and the rest of our existing upgrade scripting works. If we discover issues that need to be addressed first, they will likely delay the effort until 16.1 or later due to other responsibilities during the Major release.

Previous investigation issue can be found here: #5508 (closed)

Investigation steps:

• Confirm upstream rails QA tests pass with PG14 - gitlab!114624 (merged)
• Confirm omnibus can build and run PG14, an that qa tests pass

Typical logged issue outcomes:

• Add PG 14 as opt-in for fresh installs - example
• Single node upgrades for PG 14 - example
• Verification issues for complex architectures (various patroni and Geo setups)