Add Hugging Face repo download endpoint

[DocShotgun]

Adds a wrapper for huggingface_hub downloader to download models/loras via API request, requires optional dependency huggingface_hub.

TODO:

• More robust reporting of errors that occur within snapshot_download such as a bad repo_id or revision, unauthorized access to a gated/private repo (currently results in a simple 500 Internal Server Error)
• Consider addition of default HF token to be used for downloading to config.yml, or reading a saved HF token from HF cache

Is your pull request related to a problem? Please describe.
N/A

Why should this feature be added?
Some users have requested the ability to download models through tabbyAPI itself. This adds a simple option that requires an optional dependency package for those who want this functionality and do not want to deal directly with huggingface-cli.

Examples
N/A

Additional context
N/A

[bdashore3]

Great feature, but the current implementation of HF hub's downloader uses threads that don't have a SIGINT event set up. Therefore, this will require some more work to get working.

Reference: huggingface/huggingface_hub#1818

[bdashore3]

Implemented in 55ccd1b