More structured logger names, #27922 (#27934)

* some cluster logging improvements
* most logger names are actually good, when using ActorLogging since
  config can be setup on the package (prefix)
* override logSource when StageLogging is used
* replace system.log with more specific logger

akka-stream/src/main/scala/akka/stream/impl/fusing/Ops.scala

@@ -1405,6 +1405,7 @@ private[stream] object Collect {
 
   override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
     new GraphStageLogic(shape) with InHandler with OutHandler with StageLogging {
+      override protected def logSource: Class[_] = classOf[Watch[_]]
 
       private lazy val self = getStageActor {
         case (_, Terminated(`targetRef`)) =>