Move to pydata theme for unification

[scriptautomate-bc]

Summary

Adds and expands on the pydata theme currently used on the 3008 reference docs:

• Collapsible left-hand TOC nav items
• Better formatted/spaced left-hand TOC nav items
• Instead of "Table of Contents", will be the name of the specific docset (ex. "Salt User Guide")
• Top nav will have a color change meaning "Active" so that you can tell which docset you are on (ex. "User Guide" highlighted because on those docs)

Related

• Fixes Migrate Sphinx theme from Furo to pydata #9
• Related: [DOCS] Salt Reference Docs: Sphinx Theme Refresh (Furo, Sphinx Book, or Alternative Third-Party Managed Theme) and Deprecation of saltstack2 custom theme salt#67090
  • Builds on work from: Migrate documentation to PyData Sphinx Theme salt#69185