Generate API docs from code with sphinx autodoc (#2699)

Expanding on the addition of docstrings in code, this adds python module API docs to sphinx documentation.

A developer can preview what this might look like by running this locally:

```
tox -m docs
```

The option `-W` is added to the tox env so that warning messages are considered errors.

Adds doc generation using the above method to the test GitHub workflow to catch documentation problems on PRs.

Some docstrings have been reformatted and fixed to satisfy errors generated with the above setup.

requirements.docs.txt

@@ -0,0 +1,5 @@
+sphinx>=4
+sphinx_rtd_theme
+sphinxcontrib-apidoc
+sphinx-github-style
+pyyaml