DOC: Merge extraheader block from theme instead of override (#70187)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/70185
The extraheader block in docs/source/_templates/layout.html overrides the one from the pytorch theme. The theme block adds Google Analytics, so they were missing from the `master` documentation. This came up in PR pytorch/pytorch.github.io#899.
brianjo
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70187
Reviewed By: bdhirsh
Differential Revision: D33248466
Pulled By: malfet
fbshipit-source-id: b314916a3f0789b6617cf9ba6bd938bf5ca27242
