[Doctrine ORM] Changed type to attribute (#2966)

Author: mnocon

docs/administration/configuration/repository_configuration.md

@@ -76,7 +76,7 @@ ibexa:
         entity_mappings:
             IbexaCoreBundle:
                 is_bundle: true
-                type: annotation
+                type: attribute
                 dir: Entity
                 prefix: Ibexa\Bundle\Core\Entity
 ```