Centralize common headers, this will help up to move biz metrics out of the process

lib/api/middlewares/user.js

@@ -18,7 +18,7 @@ module.exports = function user (metadataBackend) {
             }
 
             res.locals.userId = userId;
-            res.set('Carto-User-Id', `${userId}`);
+
             return next();
         });
     };