=doc #15538 Updating documentation on deliver and confirmDelivery

=doc #15538 Updating the documentation on deliver and confirmDelivery in the persistence for Scala, Java and Lambda-java
This "Deliver also requires a function that can specify the delivery id for the message." is not correct. The function `deliveryIdToMessage: Long ⇒ Any` gets the deliveryId as parameter and returns the message.
It is not a function to generate the deliveryId. Normally you will pass the deliveryId in the message, and send it back in the confirmation message, but that is up to the user.