Add layout.html to template for stable docs (#33770)
Summary:
When docs are built, conf.py points to a _templates-stable/layout.html that does not exist.
Adding this file here so future stable docs will build with Google Analytics tags and without the unstable able that is in _templates/layout.html
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33770
Differential Revision: D20164895
Pulled By: jlin27
fbshipit-source-id: 5fca9f9b825b1484dab52e2b2d91f92ae6372371
