* 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
* ignore PubSub Status message from unknown node, #20846
Reproducer:
1. old cluster of node1, node2 and node3
2. shutdown node3 and start it again with same host:port, let it
join itself and not the old cluster
3. node1 and node2 will continue to gossip to the node3 address and
Status message is accepted and replied to (Delta is ignored from
unknown node)
Solution:
* ignore status message from unknown node
* also added a reply flag in the Status message to break the
back-and-forth replies in case the deltas are not accepted,
this is not needed for fixing this bug, but it adds an extra
level of safety
