docs: readthedocs theme (#33116)

* docs: read the docs theme

* nav depth
old-commit-hash: 691b948ad02a20e507d5059707f8cde51a94a703

.github/workflows/docs.yaml

@@ -29,7 +29,7 @@ jobs:
     - name: Build docs
       run: |
         # TODO: can we install just the "docs" dependency group without the normal deps?
-        pip install mkdocs mkdocs-terminal
+        pip install mkdocs
         mkdocs build
 
     # Push to docs.comma.ai