[dist_optim] add distributed functional rprop optimizer (#55834)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55834
ghstack-source-id: 126325536
Reviewed By: rohan-varma
Differential Revision: D27703878
fbshipit-source-id: 5c8ec9a4ccb4442b2b51d48d75ea5cd506179f14
