Updated error when _APP_USAGE_STATS is disabled

for usage

app/controllers/api/projects.php

@@ -268,6 +268,9 @@ App::get('/v1/projects/:projectId/usage')
         }
 
         $usage = [];
+        if (App::getEnv('_APP_USAGE_STATS', 'enabled') != 'enabled') {
+            throw new Exception(Exception::GENERAL_USAGE_DISABLED);
+        }
         if (App::getEnv('_APP_USAGE_STATS', 'enabled') == 'enabled') {
             $periods = [
                 '24h' => [