Add XNNPACK with and without quantization tests to CI (#123)

Summary:
TSIA. After https://github.com/pytorch/executorch/pull/122, we can now add XNNPACK tests to CI.  Note that `xnn_executor_runner` is only available via buck2 here, its cmake support will come in the next PR.

Pull Request resolved: https://github.com/pytorch/executorch/pull/123

Test Plan:
Spot check for `add` example which supports both XNNPACK and quantization.  Both are tested:

Linux: https://github.com/pytorch/executorch/actions/runs/5970562477/job/16198874573?pr=123
MacOS: https://github.com/pytorch/executorch/actions/runs/5970562477/job/16198877840?pr=123

Reviewed By: guangy10, kirklandsign

Differential Revision: D48670404

Pulled By: huydhn

fbshipit-source-id: 51974887cce141d9abccf3581f5003dfb23fe53d