[Configs] Add EnableValidationAttributesRector

[TomasVotruba]

Adds EnableValidationAttributesRector to the configs set.

When validation metadata is moved from loadValidatorMetadata() to attributes (see LoadValidatorMetadataToAttributeRector), the framework config must load them. This rule flips the config value:

 $container->loadFromExtension('framework', [
     'secret' => '%secret_key%',
     'validation' => [
-        'enable_attributes' => false,
+        'enable_attributes' => true,
     ],
 ]);

Scope:

• matches $container->loadFromExtension('framework', [...]) array config only
• only flips an existing false value, does not add a missing key