Save drop item media

Deprecated: use POST /api/v2/drops/{slug}/items/media/save-batch, which saves the same items by upload_batch_id and filename. This operation will be removed. Until then it works, but it sends every media token back and checks each file separately, so it slows down with drop size.

Saves the drop's items from media tokens issued by POST /api/v2/drops/{slug}/items/media and uploaded to storage. Each save replaces the drop's items rather than adding to them. With a manifest from POST /api/v2/drops/{slug}/items/manifest, items take their token ids and metadata from it; without one they are numbered 1 to n in the order given.

Not available on ERC-1155 self-mint drops, which return 400: create each of their items with POST /api/v2/drops/{slug}/items.