FR: Reduce margins in the service configuration form (see #932)

See #932 for context. This is suggestion 4.

It's nice to have a well-spaced interface, but with the various top banners, it forces a lot of scrolling and prevents getting a quick overall view of the form. It would be useful to reduce margins (mostly vertical margins) so that the configuration can be more efficiently browsed without having to scroll so much.

Below a suggestion of a target interface that, in my opinion, would be more usable, IMO.