[NCCL] create NCCL communicator for send/recv on demand (#44922)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44922
For NCCL send/recv operations, we will create NCCL communicator on demand following the same design as how it's currently done for collective operations.
ghstack-source-id: 113592757
Test Plan: to add
Reviewed By: pritamdamania87
Differential Revision: D23773726
fbshipit-source-id: 0d47c29d670ddc07f7181e8485af0e02e2c9cfaf
