Indicate when uploading has successfully completed

[bfirsh]

Why

Replicate current displays when it is starting to upload things to the background. This is useful so you can understand what Replicate is doing, and so you can correlate the checkpoint ID with your own output.

But there is no clear confirmation of content being uploaded successfully. You have to trust that Replicate has done its job properly and hasn't silently failed for some reason. The fact it is done in the background with little log output does not feel robust.

How

Needs design. How can we do this without being too verbose?

Related

This is a follow-on of the work in #408