feat: Add toggle for vertical workspaces

[ids1024]

This adds a toggle for enabling/disabling vertical workspaces on Gnome 40. We've mentioned supporting it. If we're satisfied with just enabling/disabling the vertical-overview extension (as done here), it's not too hard to support. Though we will want to test that Cosmic works well with or without it enabled.

Not sure if there's a better UI for this.

I'm not sure what thoughts @maria-komarova and @WatchMkr have about where this would best fit in settings.