Add dispatch keys for out-of-tree grad+vmap prototype (#56824)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56824
This PR adds 6 dispatch uses to be used with prototyping.
I'm not sure what the best way to name these are, please let me know if
you think that these should have the same prefix.
Test Plan: - wait for tests
Reviewed By: driazati
Differential Revision: D27999963
Pulled By: zou3519
fbshipit-source-id: 0c3ef4788854f7a93d077cc454b773a6eedbbc22
