Add padding around edge labels

[i-am-the-slime]

In #2030 there's an example of a somewhat good-looking diagram. It has padding around edge labels.
The same goes for #920 . The current padding is so tight, that with certain fonts and settings (#1099) the text becomes unreadable.
I was hoping that as a workaround it'd be possible to just prefix and suffix the labels with a space character but that also doesn't work.

Rather, the opposite is true as can be witnessed in this example: