Send email notification on task creation and completion

As far as I know, there are currently no notifications related to pull request tasks. When creating a task in response to a reviewer comment, I would like to send an email notification to let that reviewer (and the other watchers) know that the comment is going to be addressed or has been addressed. Right now, I have to create the task and then add a comment noting that I agree with the suggested change or that the change was completed.

As noted in STASH-4496, it would be beneficial to be able to turn these notifications on/off.