Prepare a remote text/data file for input to a chat.
Use this for plain text, Markdown, CSV, code, and other non-PDF documents hosted at a URL (use content_pdf_url for PDFs). Not all providers accept every document type, so check the documentation for the provider you are using.
The document’s MIME type. If "auto", it’s guessed from the URL’s file extension, falling back to "text/plain". data: URLs always use the type declared in the URL itself.