Add files to an unsent transfer

Files you will upload yourself.

Files Yungle fetches from URLs itself, so the bytes never pass through you. Up to 20 per call. Each is created like an upload (quota, size ceilings, API metering) and imported in the background; follow it with GET /imports/{fileId}.

One per entry in files, in the same order.

One per entry in imports, in the same order. Empty when none were sent.