organize verbatim sources with subdirectories (#38688)
Summary:
re-use master-only branch filter logic and docker constants
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38688
Differential Revision: D21634022
Pulled By: kostmo
fbshipit-source-id: 8a47af7fb08fb77e8f2ea376b564a84abca1ad50
