[DataPipe] implementing fork() (#63649)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/63649
Test Plan: Imported from OSS
Reviewed By: ejguan
Differential Revision: D30493945
Pulled By: NivekT
fbshipit-source-id: 40db7d4134facd266d86bc0dc2edf2729c4e5842
