Add userbenchmark support to TorchBench CI (#78794)
Support userbenchmarks, such as nvfuser, in the TorchBench CI.
Test Plan: TorchBench CI
RUN_TORCHBENCH: nvfuser
TORCHBENCH_BRANCH: xz9/fix-ubs
Pull Request resolved: https://github.com/pytorch/pytorch/pull/78794
Approved by: https://github.com/malfet
