Generate a Signed URL to upload files 32MB or larger. Uploading via the signed URL writes the file to the storage bucket only — it does not create a database record. After a successful upload, call Create Media File with the same filename and the bin_id value in the insstance to create the record; without this step the file won't appear in the media library or be queryable via the API. For files under 32MB, use Upload a File Asset instead, which creates the record automatically.