Integrate DB test process into release, update DB requirements

[ssddanbrown]

In this folder I added a docker-based testing process to run though major versions of supported databases, and run our full test suite against each.

This should be added to the release-steps devops script, as something to run manually before release where DB affecting changes have been made. Needs a little extra clean-up to allow full test suite to work in the designed docker-based environment, and needs documentation to cover its use.

We should also update our required DB versions on the project install page, just to trim off very old unsupported DB versions, and to reduce what we need to test against.

Docs Updates

• Update requirements on install page with those decided upon.
  • MySQL 8.0
  • MariaDB 10.6
• Update advisory for min-supported DB version change.

[ssddanbrown]

Added to release steps: https://codeberg.org/bookstack/devops/commit/6883aa7674839d77ab1af20ce97ca419de24e28e

[ssddanbrown]

Added readme and further cleanup, and DB version changes, of testing setup in 870f3c5

Changes min. supported MySQL to 8.0, and MariaDB to 10.6