+per #17579 #17617 Introduces EventAdapter

+ per plugin scoped adapters
+ could be swapped during runtime
+per EventAdapter now has manifest and is configurable ai la serializers
+ json examples in docs
+ including "completely manual" example in case one wants to add
  metadata TO the persisted event
+ better error reporting when misconfigured bindings
+ manifest is handled by in memory plugin
- did not check if it works with LevelDB plugin yet
> TODO: json example uses Gson, as that's simplest to do, can we use
+per allows 1:n adapters, multiple adapters can be bound to 1 class

akka-docs/rst/scala/code/docs/persistence/PersistencePluginDocSpec.scala

@@ -92,6 +92,9 @@ object SharedLeveldbPluginDocSpec {
       //#shared-store-config
       akka.persistence.journal.leveldb-shared.store.dir = "target/shared"
       //#shared-store-config
+      //#event-adapter-config
+      akka.persistence.journal.leveldb-shared.adapter = "com.example.MyAdapter"
+      //#event-adapter-config
     """
 
   //#shared-store-usage