Add GGUF as supported expand[] parameter

[Wauplin]

Follow-up after https://github.com/huggingface-internal/moon-landing/pull/11060 and https://github.com/huggingface-internal/moon-landing/pull/11112 (internal links).

This PR adds support for the gguf key in ModelInfo. Also documenting it as supported in expand[]= parameter. Note that it was supported as soon as the server-side change is made, this PR simply makes it better documented.

Example:

>>> from huggingface_hub import model_info
>>> model = model_info("MaziyarPanahi/solar-pro-preview-instruct-GGUF", expand="gguf")
>>> model.gguf
{'total': 22140032000, 'architecture': 'llama', 'context_length': 4096, 'quantize_imatrix_file': './solar-pro-preview-instruct-GGUF_imatrix.dat', 'chat_template': "{% if not add_generation_prompt is defined %}{% set add_generation_prompt = false %}{% endif %}{% for message in messages %}{{'<|im_start|>' + message['role'] + '\n' + message['content'] + '<|im_end|>' + '\n'}}{% endfor %}{% if add_generation_prompt %}{{ '<|im_start|>assistant\n' }}{% endif %}"}

[hanouticelina]

Seems like a concurrent PR with @hlky's #2544 😄

[hanouticelina]

LGTM 👍 thanks!