Implement Delete effect for DurableState

[patriknw]

DeletedDurableState in the query.

Also implement deleteObject(persistenceId: String, revision: Long) correctly, so that it keeps latest record but updates payload to null. Similar to how events are deleted. When loading it should continue from latest revision even if it is deleted.

See akka/akka#31529

[leviramsey]

Seems completed?

[patriknw]

I think something is still missing in the implementation

akka-persistence-jdbc/core/src/main/scala/akka/persistence/jdbc/state/scaladsl/JdbcDurableStateStore.scala

Line 109 in 500642d

// FIXME #686 use revision

[danieltahara]

Just hit this I think

If you perform Effect.delete but don't stop the actor, then actor expects its sequence number is incremented so any subsequent update fails.

However, the DB expects that the sequence number should be 1 b/c it doesn't have a row in the database. The actor is now wedged.