Update dev and test configs to streamline developer experience

[AdamHawtin]

What is the context of this PR?

Update the development and test defaults, so that running the app and tests locally works out of the box, without setting additional environment variables. Developing and testing in the docker container should also still work with no addtional steps, as the compose file already overrides the environment variables to its needs.

How to review

• Check out this branch locally
• Remove or rename any previous .env files or environment configuration you previously had for native local development
• Follow the README steps for "Running locally with supporting services in Docker"
• Try to start the app locally, either from your shell or IDE of choice
• Check the app runs successfully without you having to configure additional environment variables (other than setting the DJANGO_SETTINGS_MODULE, if you are running by a method other than the make runserver command, as the README says).
• Run the unit/component tests locally. Note there may be an unrelated issue with running the tests in the parallel locally with the make test command, if this fails with an error try running poetry run coverage run ./manage.py test --shuffle --settings=cms.settings.test instead to run them in series.
• Stop the locally running app
• Try running the app and tests in the docker container, following the README instructions, to check the config changes haven't broken that method.

Follow-up Actions

None

[nehakerung]

LGTM - followed instructions which worked 🫡

[zerolab]

A couple of very minor suggestions, otherwise it works well.

Locally have to use poetry run ./manage.py test ... as make test does fail with AttributeError: 'DatabaseWrapper' object has no attribute '_test_serialized_contents' and while tempting, we have many other tasks to get on with

[zerolab]

This is marked improvement. 👍🏼 from me