[Opt Overlap] Implement register_fused_optim in DDP (#71606)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71606
Per title
ghstack-source-id: 147577172
Test Plan: CI
Reviewed By: cbalioglu
Differential Revision: D33694037
fbshipit-source-id: a148d5ce6031f0cc20f33785cfe2c27d1fc2d682
(cherry picked from commit ace3261e0cd6898e3203cf30e78e17e80e5fc42f)
