Add remote_parameters() into RemoteModule class. (#43906)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43906
This method returns a list of RRefs of remote parameters that can be fed into the DistributedOptimizer.
Original PR issue: RemoteModule enhancements #40550
Test Plan: buck test caffe2/test/distributed/rpc:process_group_agent -- RemoteModule
Reviewed By: rohan-varma
Differential Revision: D23399586
fbshipit-source-id: 4b0f1ccf2e47c8a9e4f79cb2c8668f3cdbdff820
