add isNotificationScheduled resolver and test cases

src/resolvers/QueryResolvers.ts

@@ -15,6 +15,9 @@ export const QueryResolvers: Resolvers<ServerContext> = {
         name: system.name,
         id: system.id,
       };
+    },
+    isNotificationScheduled: async (_parent, args, contextValue, _info) => {
+      return false;
     }
   },
-}
+}