Materializer settings as attributes (#27499)

* Replace MaterializerSettings with Attributes #25559 
 * Field access to settings deprecated to make stages use attributes instead
 * Internal stages updated to use attributes
 * Docs on ActorMaterializerSettings updated to recommend away from using it
 * Verify all stages stopped after each testcase in FlowGroupBySpec
 * Subscription timeout attributes merged into one

akka-stream/src/main/scala/akka/stream/impl/QueueSource.scala

@@ -45,7 +45,7 @@ import scala.concurrent.{ Future, Promise }
       var terminating = false
 
       override def preStart(): Unit = {
-        if (maxBuffer > 0) buffer = Buffer(maxBuffer, materializer)
+        if (maxBuffer > 0) buffer = Buffer(maxBuffer, inheritedAttributes)
       }
       override def postStop(): Unit = {
         val exception = new StreamDetachedException()