enable_annotations is enabled by default

Not sure at 100% of the use of `FullStack` means, but in a default Symfony app `enable_annotations` is always true.

```bash
php bin/console config:dump-reference framework
```

```yaml
    validation:
        enabled:              true
        cache:                ~
        enable_annotations:   true

    # serializer configuration
    serializer:
        enabled:              true
        enable_annotations:   true
```

Author: bastnic

reference/configuration/framework.rst

@@ -2512,7 +2512,7 @@ settings is configured.
 enable_annotations
 ..................
 
-**type**: ``boolean`` **default**: ``false``
+**type**: ``boolean`` **default**: ``true``
 
 If this option is enabled, validation constraints can be defined using annotations or attributes.
 
@@ -2720,7 +2720,7 @@ Whether to enable the ``serializer`` service or not in the service container.
 enable_annotations
 ..................
 
-**type**: ``boolean`` **default**: ``false``
+**type**: ``boolean`` **default**: ``true``
 
 If this option is enabled, serialization groups can be defined using annotations or attributes.