Dynamic registration of RPC backends (#25734)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25734
[pytorch] Dynamic registration of RPC backends
Allow non-pg rpc backends to be plugged in as a backend.
ghstack-source-id: 89938296
Differential Revision: D17183789
fbshipit-source-id: 885fed12d80b82b60f9a125f78302a161e708089
