Option to run docker with or without pytest

[docsteveharris]

It would be useful to be able to write tests that will run depending on the context.
That is

• tests that run against live data
• tests that run against mock data

For now, I've just added the [test] suffix to the pip install command in the docker file for the API

# installs testing: useful for debugging
RUN pip install --no-cache-dir /app/api[test]
# without testing
#RUN pip install --no-cache-dir /app/api

But I think the Dockerfile should pick up an environment file and this might both affect the pip install step, and be used to select/filter the tests that run.

We should also think about running these tests during the docker build?
That way we would have some reassurance that dockerised version will work as expected.
It would be nice to also work toward an end-to-end test that checked the status of the front-end too (as per the original playwright work).

[docsteveharris]

See 4f6aee2 for some early work