* Provide shorter aliases for the ActorRefProviders #20649
* Use the new actorefprovider aliases throughout code and docs
* Cleaner alias replacement logic
Allows the cluster client and its receptionist to be observable in terms of contact points becoming available and client heartbeats. Furthermore a query API for requesting the current state has been provided.
* number-of-contacts is by default 3, and in this test
with 4 server nodes we shutdown all but one in the end
and sometimes the client has all other except the remaining
node in its list of contacts, so it will never get contact
with the remaining node
* because it will result in quarantine if failure
detection triggers and that kind of coupling is
exactly what is not desired for a ClusterClient
* replace by simple heartbeat failure detection,
DeadlineFailureDetector
* DeadLetterSuppression
