add CoordinatedShutdown, #21537

* CoordinatedShutdown that can run tasks for configured phases in order (DAG)
* coordinate handover/shutdown of singleton with cluster exiting/shutdown
* phase config obj with depends-on list
* integrate graceful leaving of sharding in coordinated shutdown
* add timeout and recover
* add some missing artery ports to tests
* leave via CoordinatedShutdown.run
* optionally exit-jvm in last phase
* run via jvm shutdown hook
* send ExitingConfirmed to leader before shutdown of Exiting
  to not have to wait for failure detector to mark it as
  unreachable before removing
* the unreachable signal is still kept as a safe guard if
  message is lost or leader dies
* PhaseClusterExiting vs MemberExited in ClusterSingletonManager
* terminate ActorSystem when cluster shutdown (via Down)
* add more predefined and custom phases
* reference documentation
* migration guide
* problem when the leader order was sys2, sys1, sys3,
  then sys3 could not perform it's duties and move Leving sys1 to
  Exiting because it was observing sys1 as unreachable
* exclude Leaving with exitingConfirmed from convergence condidtion

akka-distributed-data/src/test/resources/reference.conf

@@ -3,3 +3,7 @@ akka.actor {
   serialize-creators = on
   warn-about-java-serializer-usage = off
 }
+
+akka.coordinated-shutdown.run-by-jvm-shutdown-hook = off
+akka.coordinated-shutdown.terminate-actor-system = off
+akka.cluster.run-coordinated-shutdown-when-down = off