Add pybind trampoline for ProcessGroup and Work (#66338)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66338
This commit exposes c10d extension API to Python land. Users can
now override c10d communication behaviors in pure Python, and no
longer needs to go through the cpp extension steps.
Test Plan: Imported from OSS
Reviewed By: rohan-varma
Differential Revision: D31514351
Pulled By: mrshenli
fbshipit-source-id: a8b94af0af7960c078e1006c29b25f7f3bd86c81
