Missing Google Analytics from the pytorch-sphinx-theme in rendered docs

[mattip]

📚 The doc issue

Google Analytics are missing from the master documentation and from PR pytorch/pytorch.github.io#899

The extrahead stanza from the theme is missing in rendered docs. PR 58056 added a {% block extrahead %} stanza that overrides the one in the theme.

Suggest a potential alternative/fix

The block should add a {{ super() }} line to the extrahead stanza in docs/source/_templates/layout.html. PR incoming.

layout.html contains a number of other blocks: menu, sidebartitle, and footer. Those should also be examined to see if they should merge content or override.

cc @brianjo @mruberry