Implement reStructured Text Linting on docstrings and docs

[kylie-bee]

Implement docstring linting via Flake8 extensions:

• flake8-docstrings
• flake8-rst-docstrings

And documentation linting via new CLI tool sphinx-lint and the dummy builder for sphinx-build.

Initial implementation does not include doc string linting in GitHub action jobs (i.e., this does not change what is required to publish changes). New parameter turns on exit on failed checks which is set when building.

Fixes #552