Automating formatting for official D repos

[Prajwal S N]

I came across this suggestion from Rikki in one of the other 
threads, and just wanna make sure I understand correctly - we'd 
ideally want a CI job that runs dfmt on the PR, and in case of 
any reformatting, it pushes a commit with those changes. Or are 
we just looking for a job that detects if there is something 
that's not formatted correctly? (I think we already have this? 
Not sure)