add `OpInfo` for `torch.diagflat` (#65680)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65680
cc mruberry
Test Plan: Imported from OSS
Reviewed By: pbelevich
Differential Revision: D31730001
Pulled By: mruberry
fbshipit-source-id: 487e41da4b043944cc5b26d6081209fb0875f4de
