Iterative review: pre-commit transition to post-commit

This is related to CRUC-2998. Where CRUC-2998 focuses only on iterative pre-commit reviews, this feature would allow iteration of the review to continue with a post-commit changeset.

Something that I've run into a few times is that it is not uncommon for us that a review begins as pre-commit but we would really like to iterate on it post commit. This lets those potentially ugly changes start off a bit safer (pre-commit review) but then once they've had a chance for at least a first pass or two of changes be committed and reviewed with the benefits of a regular iterative review.