First implementation of DurableStateBehavior, #30277

* implementation is based on a copy of the EventSourcedBehavior and then
  refactoring all things that are not needed or different such as:
  * remove replicated event sourcing
  * remove ReplayingEvents recovery phase
  * remove retention and snapshotting
  * remove SnapshotSelectionCriteria and snapshots
  * remove PersistAll
  * remove event handler, event types
  * rename EventSourced
  * single static tag
  * DurableStateAdapter
  * DurableStateSignal

* DurableStateStore plugin api with similar extension mechanism as query plugins
  * DurableStateStore, DurableStateUpdateStore
  * DurableStateStoreQuery

* note that the DurableStateStore can be pretty useful for other things also

akka-persistence-query/src/main/scala/akka/persistence/query/DurableStateChange.scala

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2021 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package akka.persistence.query
+
+/**
+ * @param persistenceId The persistence id of the origin entity.
+ * @param seqNr The sequence number from the origin entity.
+ * @param value The object value.
+ * @param offset The offset that can be used in next `changes` or `currentChanges` query.
+ * @param timestamp The time the state was stored, in milliseconds since midnight, January 1, 1970 UTC
+ *   (same as `System.currentTimeMillis`).
+ *
+ * @tparam A the type of the value
+ */
+final class DurableStateChange[A](
+    val persistenceId: String,
+    val seqNr: Long,
+    val value: A,
+    val offset: Offset,
+    val timestamp: Long)