MQTT streaming: Fixes wrong Exception thrown when client ping timeouts (

#1642)

## Purpose

When mqtt client doesn't send ping request within the expected period (given by the connect keep alive parameter) stream should failed with `ServerConnector.PingFailed` exception but it fails with `ClientConnection.PingFailed` exception. That makes that ActorMqttServerSession command flow doesn't translate the failure to the public api error ActorMqttServerSession.PingFailed (MqttSession.scala::482)

## Background Context

There was an ignored failing unit test due to this bug that however was pointing to a different issue. After this PR this unit test is not failing anymore so I activate it again.

mqtt-streaming/src/main/scala/akka/stream/alpakka/mqtt/streaming/impl/ServerState.scala

@@ -11,6 +11,7 @@ import akka.{Done, NotUsed}
 import akka.actor.typed.scaladsl.{ActorContext, Behaviors}
 import akka.actor.typed.{ActorRef, Behavior, ChildFailed, PostStop, Terminated}
 import akka.annotation.InternalApi
+import akka.stream.alpakka.mqtt.streaming.impl.ServerConnector.PingFailed
 import akka.stream.{Materializer, OverflowStrategy}
 import akka.stream.scaladsl.{BroadcastHub, Keep, Source, SourceQueueWithComplete}
 import akka.util.ByteString
@@ -619,7 +620,7 @@ import scala.util.{Failure, Success}
             local.success(ForwardPingReq)
             clientConnected(data)
           case (context, ReceivePingReqTimeout) =>
-            data.remote.fail(PingFailed)
+            data.remote.fail(ServerConnector.PingFailed)
             timer.cancel(ReceivePingreq)
             disconnect(context, data.remote, data)
           case (context, DisconnectReceivedFromRemote(local)) =>

mqtt-streaming/src/test/scala/docs/scaladsl/MqttSessionSpec.scala

@@ -21,6 +21,7 @@ import akka.testkit._
 import akka.util.{ByteString, Timeout}
 import org.scalatest.{BeforeAndAfterAll, Matchers, WordSpecLike}
 import org.scalatest.concurrent.ScalaFutures
+import org.scalatest.time.{Millis, Span}
 
 import scala.concurrent.{ExecutionContext, Promise}
 import scala.concurrent.duration._
@@ -1514,7 +1515,11 @@ class MqttSessionSpec
       server.watchCompletion().foreach(_ => session.shutdown())
     }
 
-    "close when no ping request received" ignore { // assertAllStagesStopped { // https://github.com/akka/alpakka/issues/1563
+    "close when no ping request received" in assertAllStagesStopped {
+      // A longer patience config implicit is provided since minimum client's keep alive time is 1 second, so default
+      // 150 millis is not enough for the ping request timeout to be triggered and verify the stream fails as expected.
+      implicit val patienceConfig = PatienceConfig(scaled(Span(3000, Millis)), scaled(Span(15, Millis)))
+
       val session = ActorMqttServerSession(settings)
 
       val client = TestProbe()