Update assets

Update up to BATCH_MAX_ITEMS assets in a single request.

title is the only writable attribute; it is persisted to the asset's display name. type, state, status_msg and download_url are server-owned and a client that sends them has them silently ignored rather than rejected.

Returns 200 if all items succeed, 207 if any fail, 400 if the envelope is empty or over the cap.

Required OAuth scope: assets:write