Add option for segment gap

[Elias-Graf]

When the menu is "centered", (also called "gap between panel and screen edges" in the settings), it would be nice if there was some (configurable?) gap between the segments.

[git-f0x]

I think this would be better as a toggle that says something like Separate panel segments, that makes the panel fill in just the segments, rather than the entire width, with the non-expanded spacing probably matching the gap.
It would also enable visually moving the panel to just a corner, as mentioned in pop-os/cosmic-epoch#653.

[Elias-Graf]

So you would have three different "bubbles"? Sure, that sounds like a good option, but I still wouldn't mind a slider or input, in which I can set my panel gap in.

But if the goal is not to have too many different settings, what you said would definitely help in identifying what content is in what section.