Feature/redbox 73 unit test core api

[gecBurton]

Context

We want to unit test the core-api so that we have confidence that the code is working as expected.

Changes proposed in this pull request

1. I have added unit test for the core-api
2. I have renamed the core-api endpoints to make the more RESTful https://stackoverflow.blog/2020/03/02/best-practices-for-rest-api-design/
3. In other parts of the code we were (I was!) erroneously force loading the .env.test when we should be leaving it up to pydantic-settings to work put where the .env file is

Guidance to review

• do the new tests make sense

Note - there is a lot of duplication of code between the various conftests - I have ignored this for now as I am not sure what we should do about it, if anything.

Relevant links

https://technologyprogramme.atlassian.net/browse/REDBOX-73

Things to check

• I have added any new ENV vars in all deployed environments
• I have tested any code added or changed

[lmwilkigov]

I like the look of the tests! Just did a minor fix in the actions YAML to call them.