Install sphinx from docs/requirements.

[delucchi-cmu]

Change Description

Closes #431 .

Adds lines in setup scripts to install all dependencies in docs/requirements, so we're not maintaining the list of docs requirements in two places. Removes those dependencies from pyproject.toml, and also alpha-sorts the current dependencies list (because it irks me that a freshly-minted project is unsorted).

Checklist

• This PR is meant for the lincc-frameworks/python-project-template repo and not a downstream one instead.
• This change is linked to an open issue
• This change includes integration testing, or is small enough to be covered by existing tests

[hombit]

Thank you!