=clu #15412 Add paths(system) method to Group router

to be able to use the role correctly in cluster aware routers

This solution is very similar to what we did for nrOfInstances
in Pool routers.

akka-actor/src/main/scala/akka/routing/Random.scala

@@ -135,6 +135,8 @@ final case class RandomGroup(
    */
   def this(routeePaths: java.lang.Iterable[String]) = this(paths = immutableSeq(routeePaths))
 
+  override def paths(system: ActorSystem): immutable.Iterable[String] = this.paths
+
   override def createRouter(system: ActorSystem): Router = new Router(RandomRoutingLogic())
 
   /**