Print a PG 11 deprecation notice when upgrading with an external database
Summary
In GitLab %13.6, PostgreSQL 12 will become the default version for upgrades. A user can still opt to stay on PostgreSQL 11 during an upgrade, but if they do, we should warn them that they will need to upgrade PostgreSQL by GitLab 14.0 when PostgreSQL 12 becomes the minimum required version. This issue is specifically for upgrades that involve an external PostgreSQL database.
Proposal
During reconfigure on rails nodes, query the database for its version, and if less than 12 print a warning.
The warning should read: "Note that PostgreSQL 12 will become the minimum required PostgreSQL version in GitLab 14.0 (add release date). PostgreSQL 11 will be removed and no longer supported in GitLab 14.0. Please consider upgrading your PostgreSQL version soon."
Requirements
The notice should print when a user runs sudo apt-get update
but opts out of upgrading PostgreSQL
Issue used when removing PG 10: #5096 (closed)