* Retry creation of ActorSystem in remoting tests #23481
Remoting multi-jvm test rely on setting port = 0 which selects an open
port. This has a race where two of the JVMs open/close the same port
then configure their ActorSystem with it so one of them fails to start
due to the port being in use. This adds a simple retry so another port
is selected.
* speedup ActorCreationPerfSpec
* reduce iterations in ConsistencySpec
* tag SupervisorHierarchySpec as LongRunningTest
* various small speedups and tagging in actor-tests
* speedup expectNoMsg in stream-tests
* tag FramingSpec, and reduce iterations
* speedup QueueSourceSpec
* tag some stream-tests
* reduce iterations in persistence.PerformanceSpec
* reduce iterations in some cluster perf tests
* tag RemoteWatcherSpec
* tag InterpreterStressSpec
* remove LongRunning from ClusterConsistentHashingRouterSpec
* sys property to disable multi-jvm tests in test
* actually disable multi-node tests in validatePullRequest
* doc sbt flags in CONTRIBUTING
* addunidoc task via an AutoPlugin that depends on PrValidation and Unidoc autoplugins
* separate cli option logic to a case class
* remove autoplugin for root project
