pyos-sphinx-theme - Create docs build infrastructure

[lwasser]

This theme will eventually be used across our packaging guide, handbook and peer review guide.
The next step is for someone to test out that the theme works here in this repo.

the tasks for this will be

1. test out the theme locally - do the docs build locally?
2. create a ci workflow that publishes the docs to gh pages using the theme.
3. if that works then we can publish this as a package to pypi (a separate task that i will create now)