Upload a knowledge file

Accepted types: pdf, doc, docx, png, jpg, jpeg, plus csv and xlsx when Meta enabled extraction on the asset. Meta's limit is 100 MB. Two ways to send the file:

• JSON { url, fileName }: Zernio downloads the file (public https URL, no redirects, capped at 100 MB) and forwards it. Use this for anything above a few megabytes.
• multipart form-data with a file part (and an optional fileName): bounded by the request body limit of about 4.5 MB; larger uploads must use the url form. Not idempotent.