Add object-based collective APIs to public docs (#48909)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48909
Adds these new APIs to the documentation
ghstack-source-id: 117965961
Test Plan: CI
Reviewed By: mrshenli
Differential Revision: D25363279
fbshipit-source-id: af6889d377f7b5f50a1a77a36ab2f700e5040150
