community/rtkit: add audio polkit authorisation

related: #13432 (comment 206423)

community/rtkit/50-rtkit.rules

+polkit.addRule(function(action, subject) {
+  if (subject.isInGroup("rtkit")) {
+      if (action.id.indexOf("org.freedesktop.RealtimeKit1.") == 0) {
+          return polkit.Result.YES;
+      }
+  }
+});