Set graphql header if method type is graphql

Author: abnegate

src/Spec/Swagger2.php

@@ -185,6 +185,10 @@ public function getMethods($service)
                         'responseModel' => $responseModel,
                     ];
 
+                    if ($output['type'] == 'graphql') {
+                        $output['headers']['x-sdk-graphql'] = "true";
+                    }
+
                     if (isset($method['consumes']) && is_array($method['consumes'])) {
                         foreach ($method['consumes'] as $consume) {
                             $output['headers']['content-type'] = $consume;