Summary:
For the release, we want to standardize on Faiss instead of FAISS.
Changed everything except the CHANGELOG.md which I assume should not be changed after it lands.
This doesn't aim to fix any existing lints / errors. Those can be handled at another time.
Reviewed By: junjieqi
Differential Revision: D68842649
fbshipit-source-id: c0b60d5baa0e1f710db3638ffcc6f223fb3408ad