Description

We've encountered users of our system that like to separate the downloading of an update from the applying of an update. I would like to add an optional flag to the docker app pull command to tell it to also pull down each of the app's service images. I have no strong opinion of what the flag would be, perhaps: docker app pull --include-services?

I don't have a complete implementation, but adding logic to pull down the images is pretty simple:
doanac@d808721