feat: cortex pull supports full HF URL download

[louis-menlo]

Problem
HF repositories do not all have the same structure, e.g., random file names, varying folder structures. I would like to download a model using an absolute model URL.

Success Criteria
When running cortex pull https://huggingface.co/BafS/gemma-2-2b-it-Q4_K_M-GGUF/blob/main/gemma-2-2b-it-q4_k_m.gguf, it should pull and run.

Additional context
Add any other context or screenshots about the feature request here.

[dan-menlo]

We can close this, in favor of @namchuai's full implementation of cortex pull here:

#1077

[dan-menlo]

Tracking as task in #1004