plasma5/systemsettings: add kirigami-addons

Some plugins fail to load if this is not in the QML import path and
simply having it as a dependency on the individual plugins does not add
it to the import path.

pkgs/desktops/plasma-5/systemsettings.nix

@@ -17,6 +17,7 @@
 , kactivities
 , kactivities-stats
 , kirigami2
+, kirigami-addons
 , kcrash
 , plasma-workspace
 }:
@@ -41,6 +42,7 @@ mkDerivation {
     kactivities
     kactivities-stats
     kirigami2
+    kirigami-addons
     kcrash
     plasma-workspace
   ];