Add support for GPTQ style INT3/4/5 quantization of LLMs like LLaMA

[powderluv]

Request description

There has been a lot of progress in low precision inference (Int3/4/5) with LLMs like LLaMA using GPTQ and llama.cpp. While we are adding support for quantization to StableHLO it would be good to ensure we can express a GPTQ quantized LLaMA via StableHLO.

It would be awesome if we added a small example of importing LLaMA form HuggingFace and exporting a GPTQ quantized StableHLO IR.

[sdasgup3]

We have started working on gathering what's needed in StableHLO to represent quantization in cutting-edge LLMs. The discussion in #1535 (comment) is pretty useful in that direction. As a starting point, we are exploring some of the int4 LLaMA / Vicuna torch IR while working with @powderluv and @qedawkins .

[sdasgup3]

I note that the GTPQ is definitely within scope of coverage along with other algorithms for the StableHLO Quantizer team. We will update the ticket once the plans are finalized.

cc @doyeonkim0