Configurable gaps

[vramdal]

I'd love to see a feature allowing me to set gaps dynamically, either

• as a CLI command

aerospace gaps outer.right=[{monitor.2 = 100}, 0]

or

• connected to a mode, e.g.

[mode.gappy.gaps]
outer.right = [{monitor.2 = 100}, 0]

[nikitabobko]

Duplicate of #1515