[RPC] Move confirmation future in rref context to jit future (#51695)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51695
As part of the plan to completely eliminate torch/csrc/utils/future.h,
we are converting this to JitFuture (c10::ivalue::Future).
ghstack-source-id: 121695708
Test Plan: CI
Reviewed By: mrshenli
Differential Revision: D26238873
fbshipit-source-id: 92bad1a349964ce8a9a80e2d1cf68f293cbe411c
