[Docs] Adding Store API Docs (#45543)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45543
This PR adds documentation for the c10d Store to the public docs. Previously these docs were missing although we exposed a lightly-used (but potentially useful) Python API for our distributed key-value store.
ghstack-source-id: 113409195
Test Plan: Will verify screenshots by building the docs.
Reviewed By: pritamdamania87
Differential Revision: D24005598
fbshipit-source-id: 45c3600e7c3f220710e99a0483a9ce921d75d044
