fix(symfony): restore graphql_playground option (#7274)

Author: soyuka

src/Symfony/Bundle/DependencyInjection/Configuration.php

@@ -266,6 +266,9 @@ private function addGraphQlSection(ArrayNodeDefinition $rootNode): void
                         ->end()
                         ->integerNode('max_query_depth')->defaultValue(20)
                         ->end()
+                        ->arrayNode('graphql_playground')
+                            ->setDeprecated('api-platform/core', '4.0')
+                        ->end()
                         ->integerNode('max_query_complexity')->defaultValue(500)
                         ->end()
                         ->scalarNode('nesting_separator')->defaultValue('_')->info('The separator to use to filter nested fields.')->end()