Merge paradox/scala/cluster-metrics.md and java/cluster-metrics.md (#23098)

* Identical contents in scala/cluster-metrics.md and java/cluster-metrics.md for easier review

* Replace java/cluster-metrics.md with a symlink to scala/cluster-metrics.md

* Fix typo

akka-docs/src/test/scala/docs/cluster/FactorialFrontend.scala

@@ -80,6 +80,7 @@ abstract class FactorialFrontend2 extends Actor {
         totalInstances = 100, routeesPaths = List("/user/factorialBackend"),
         allowLocalRoutees = true, useRole = Some("backend"))).props(),
     name = "factorialBackendRouter2")
+
   //#router-lookup-in-code
 }