Adding getDefaultFailbackDelay back to the interface

this is public interface, we can't remove methods...
It's being deprecated though

artemis-core-client/src/main/java/org/apache/activemq/artemis/api/config/ActiveMQDefaultConfiguration.java

@@ -991,6 +991,16 @@ public final class ActiveMQDefaultConfiguration {
       return DEFAULT_INITIAL_REPLICATION_SYNC_TIMEOUT;
    }
 
+   /**
+    * if we have to start as a replicated server this is the delay to wait before fail-back occurs
+    * @deprecated  use getDefaultInitialReplicationSyncTimeout()
+    */
+   @Deprecated
+   public static long getDefaultFailbackDelay() {
+      return 5000;
+   }
+
+
    /**
     * Will this backup server come live on a normal server shutdown
     */