Wrap messages in an object when responding to Iterator Next

[badtuple]

So it turns out, we don't return the message id or ingestion timestamp with the message :facepalm: . That's pretty necessary to be able to take the last message id and get the next batch.

To do that, we'll need to wrap each message in an object containing it's ID. I can't think of any other metadata to hang there, but it'd be available if we need a place to do so.