Add pydocstyle linter

[znicholls]

Add linters which check code and documentation style, see comments in .github/workflows/ci-cd-workflow.yml

[Rlamboll]

Is this done now @znicholls, or is there more to come?

[znicholls]

More to come (e.g. pydocstyle, flake8, pylint), they just all throw lots of errors at the moment so not worth the time to add yet.

[Rlamboll]

We seem to be tangling ourselves up in linter problems a lot as it is.

[znicholls]

These ones are easier to get right and significantly improve code quality and maintainability in my opinion. They do take some practice though so we can hold off for a bit.