Cumsum Converter (#66376)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66376
Added converter for cumsum and unit test
Test Plan: buck test mode/dev-nosan caffe2/torch/fb/fx2trt:test_cumsum
Reviewed By: wushirong, 842974287
Differential Revision: D31423701
fbshipit-source-id: ee3aa625d6875ba8e6bad27044d22638e99b5c03
