feat(darwin): add sketchybar to yabai module

modules/nix-darwin/yabai/sketchybar/plugins/front_app.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+# Some events send additional information specific to the event in the ${INFO}
+# variable. E.g. the front_app_switched event sends the name of the newly
+# focused application in the ${INFO} variable:
+# https://felixkratz.github.io/SketchyBar/config/events#events-and-scripting
+
+sketchybar --set ${NAME} label="${INFO}"