[HfApi] Add submit_paper endpoint

[hanouticelina]

Feature request from @NielsRogge and @AK391, slack thread here (private).

Description

Add a submit_paper() method to the HfApi class to allow authors to submit papers to Daily Papers on Hugging Face Hub. This endpoint is currently available via /api/papers/submit.

Endpoint Specs

API Endpoint: POST /api/papers/submit

inputs:

• paper_id (required): ArXiv ID of the paper to submit.
• comment (optional): Text comment about the paper.
• media_urls (optional): List of media URLs associated with the paper.

limitations:

• User must have at least one paper on HF to submit.
• cannot submit papers on weekends.
• Regular users limited to X submissions per day.
• Papers older than 7 days cannot be submitted.
• Same paper cannot be submitted twice.

The server throws HTTP errors in these cases.

Implementation Details

@validate_hf_hub_args
def submit_paper(
    self,
    paper_id: str,
    *,
    comment: Optional[str] = None, 
    media_urls: Optional[List[str]] = None,
    token: Union[bool, str, None] = None,
) -> None:
   """Submit a paper to the Daily Papers feed.

    Note:
        - You must have at least one paper on HF to submit.
        - You cannot submit papers on weekends.
        - The number of submissions per day is limited.
        - Papers older than 7 days cannot be submitted.
        - Same paper cannot be submitted twice.
    
    Args:
        paper_id (`str`):
            The ArXiv ID of the paper to submit (e.g. "2401.12345") 
        comment (`str`, *optional*):
            An optional comment about the paper
        media_urls (`List[str]`, *optional*): 
            Optional list of media URLs to attach to the submission
        token (`Union[bool, str, None]`, *optional*):
            Authentication token. Required.
    
    Returns:
        None
        
    Raises:
        - ValueError if submission criteria not met
        - HTTPError for various failure cases
    """

Tests

We still need to figure out how to run tests properly in the staging environment hub-ci. We need to have a dummy user with at least one paper submitted and find how to mock the paper submission date.
⚠️ Not sure if it's worth investing too much time on the tests here given the limited usage.