Support ONNX export Multinomial (#23581)
Summary:
cc bddppq spandantiwari
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23581
Differential Revision: D16584853
Pulled By: bddppq
fbshipit-source-id: 01c066e86a0ad071361cd67b8c3925bfb6b84a4a
