In the Milestone creation form, add a new button which copies the description of the previous milestone, for manual pasting into the Description field of the Milestone to be created.
This increases consistency of descriptions across milestones by streamlining workflows a bit.
Button texts do not wrap so it looks ugly with <600px width but hard to come up with a shorter phrase.
(Ideally the button would paste (or overwrite?) the text directly into the Milestone Description field but I'm not skilled enough to achieve that.)
Closes T15991