Update testing setup for python 3.11 and django 5.0

[mrchrisadams]

This is bit of a monster PR. I do apologise for not making it smaller.

Updates to our testing / dev setup:

• use python 3.11 as main runtime
• use uv for installing python deps, instead of pipenv
• use regular python code instead of pipenv as runner
• update gitpod accordingly
• update services in testing setup (upgrade mariadb, remove redis)
• use dotenv for managing environment variables instead of pipenv

Updates to runtime:

• use python 3.11 as main runtime
• use uv for installing python dependencies, with a dedicated build for linux
• use systemd instead of supervisord (for its native handling of env files, logging, and to remove another moving part)
• set up gunicorn to use access_log, so we see requests, and their duration in logs

Updates to Django

• Update to Django 5.0.4
• Update all the dependencies to work with django 5
• Update django admin to use the new logo (!)

[mrchrisadams]

Upgrade version of Django to current version (LTS if avaiable)

[gitpod-io]