[c10d] Move pg wrapper tests to their own file. (#59840)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/59840
moving these tests to their own standalone file. No meaningful code changes.
ghstack-source-id: 131359162
Test Plan: CI
Reviewed By: cbalioglu
Differential Revision: D29012664
fbshipit-source-id: 348870016509a6ed7e69240fa82bccef4a12d674
