add LoadSnapshotFailed in snapshot protocol, #21842

* treat snapshot load failure in same way as other recovery failures
* if load of snapshot fails the persistent actor will be stopped, since
  we can't assume that a consistent state would be recovered just by
  replaying all events, since events may have been  deleted
* additional recovery docs
* improve log message

akka-docs/rst/java/code/docs/persistence/LambdaPersistenceDocTest.java

@@ -108,6 +108,15 @@ public class LambdaPersistenceDocTest {
     }
     //#recovery-completed
 
+    abstract class MyPersistentActor6 extends AbstractPersistentActor {
+      //#recovery-no-snap
+      @Override
+      public Recovery recovery() {
+        return Recovery.create(SnapshotSelectionCriteria.none());
+      }
+      //#recovery-no-snap
+    }
+
     abstract class MyActor extends AbstractPersistentActor {
       //#backoff
       @Override

akka-docs/rst/java/code/docs/persistence/PersistenceDocTest.java

@@ -85,6 +85,15 @@ public class PersistenceDocTest {
           }
           //#recovery-completed
         }
+
+        abstract class MyPersistentActor6 extends UntypedPersistentActor {
+            //#recovery-no-snap
+            @Override
+            public Recovery recovery() {
+                return Recovery.create(SnapshotSelectionCriteria.none());
+            }
+            //#recovery-no-snap
+        }
         
         abstract class MyActor extends UntypedPersistentActor {
           //#backoff