Add server_id to getSchemaPlugin

Closes #3517264

src/GraphqlExportService.php

@@ -46,11 +46,13 @@ class GraphqlExportService {
   private function getSchemaPlugin(ServerInterface $graphql_server): SchemaPluginInterface {
     $schema_name = $graphql_server->get('schema');
 
+    $plugin_config = ['server_id' => $graphql_server->id()];
     /** @var \Drupal\graphql\Plugin\SchemaPluginInterface $plugin */
     $plugin = $this->pluginManager->createInstance($schema_name);
     $config = $graphql_server->get('schema_configuration');
     if ($plugin instanceof ConfigurableInterface && $config) {
-      $plugin->setConfiguration($config[$schema_name] ?? []);
+      $schema_config = $config[$schema_name] ?? [];
+      $plugin->setConfiguration($schema_config + $plugin_config);
     }
 
     return $plugin;