objectLoaderLoadedPartQueue
fun <T : RemoteObject<*>> objectLoaderLoadedPartQueue(): PartitionedQueue<PipelineEvent<ObjectKey, ObjectLoaderPartLoader.PartResult<T>>>
Queue between part 2 (upload parts) and part 3 (finish the upload). It will hold the fact of upload completion only, so in theory it can be Channel.UNLIMITED, but to be safe we'll limit it to 10,000 queued completions.