Allow dialing the auto-submit / don't auto-submit in the prompt

[padenot]

Following up 6422, which makes sense for @mentions, and quoting a chat discussion:

A: what was wrong with the approval flow that existed before?
B: There's a middle ground in which auto-submit depends on the source. @mention would update without asking, that's somewhat expected. The prompt could also dial this so we can express nuance between "just fix this and update the rev, it's trivial", and "get me a patch that I want to read before bugging a human"
A: Yeah, I agree with A here and miss that second version - and adding to that, I would like to be able to have hackbot iterate (or at least take initial guidance in comment form) for the patch before it makes it to "the outside world", i.e. bugzilla/phab.

[suhaibmujahid]

We could have that as an option when triggering the agent from the UI.