Add userbenchmark workflow (#1013)
Summary:
Initial commit: add userbenchmark workflow running on A100 runner.
Pull Request resolved: https://github.com/pytorch/benchmark/pull/1013
Reviewed By: FindHao
Differential Revision: D37862160
Pulled By: xuzhao9
fbshipit-source-id: df0a4aa9caddaaeb834441c3b6cd3f2268f6ce90
