WIP. Initial code to automatically upgrade PG database extensions

[justinclift]

This is initial concept code (completely untested) for automatically upgrading the extensions in the database cluster.

It needs to be tested to make sure it works at all 😁, and we'll need to add some kind of proper testing as part of our CI as well.

[justinclift]

Stumbled over something interesting today while looking at PostGIS properly for the first time (about to test it for a new project).

When upgrading PostGIS, the command to upgrade the PostGIS extensions can need to be run twice. I think it's something along the lines of the first one doing the main PostGIS extension itself, then the follow up one upgrades some optional PostGIS extensions that depend upon the first one:

https://www.cybertec-postgresql.com/en/upgrade-postgresql-postgis-together/#use-postgis-extensions-upgrade-to-finish-the-task

Looks like we'd optimally have some kind of detection for PostGIS needing to be upgraded, then handling it properly.