Add a skycastle job for ExecuTorch running llama

Summary:
As titled. This CI job covers the e2e workflow:

1. Download language_llama checkpoint, params.json and tokenizer.
2. Export *.pte file using `export_llama`.
3. Generate tokenizer from the tokenizer artifact using `tokenizer.py`
4. Run the pte file using `llama2/runner.cpp`
5. Verify the result is correct.

For starter, focus on fp32 + kv cache ~~+ xnnpack~~ combo (xnnpack runs into out of memory issue rn :()

Reviewed By: JacobSzwejbka

Differential Revision: D53580453

fbshipit-source-id: fd2b91808f436852092bd87deba00a0d6270fdc1