Add Tags property to Akka.Persistence.Query EventEnvelope

[Arkatufus]

Currently, event tags are write-only construct that were written along side of the event in question. There is no way to inspect/retrieve these tags once they are written.
It would be trivial to return these tags as part of the event metadata inside the EventEnvelope class that are returned by any of the persistence queries.
This property can be made optional (nullable) so that existing plugins can opt in on implementing it.