Create a temporary upload URL

Returns an upload_url and an id without receiving the file. Send the file's bytes as the body of a PUT request to upload_url before upload_url_expires_at, with the file's type as its Content-Type. Then attach the upload to other resources by passing its id in a JSON request body before expires_at, exactly as with an upload made by Create a temporary upload. The endpoint you attach it to checks the file against its own size and type limits, and refuses an id whose file never arrived.