!str #16484 #16392 Remove String identifier of junctions

* descriptive name can still be defined with OperationAttributes.name
* revisit all factory methods (apply/create) and implement and document
  them in a consistent manner
Merge pull request #16562 from akka/wip-16484-removed-junction-name-patriknw

!str #16484 #16392 Remove String identifier of junctions