feat(docs): add page specific last updated footer

[joshtrichards]

☑️ Resolves

Adds a "last updated" in the footer that is specific to each page. Should be locale aware.

Uses the sphinx-last-updated-by-git extension.

Caveats:

• Requires no longer doing a shallow git clone; let's see how performance looks in the PR tests before we merge

🖼️ Screenshots

New behavior: