Publish all_gather_object and gather_object docs (#43772)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/43772
Test Plan: Imported from OSS
Reviewed By: rohan-varma
Differential Revision: D23398495
Pulled By: rohan-varma
fbshipit-source-id: 032e1d628c0c0f2dec297226167471698c56b605
