Add Hook to store arbitrary python objects that are copied over in tls (#89169)
For the cudagraphs implementation, we would like to reuse objects that are defined in python across the forward and backward. The backward is run in a different thread, so to handle this we add an api for copying over arbitrary python objects in pytorch's thread local state, in the same way that C++ objects are copied over currently.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/89169
Approved by: https://github.com/albanD
