metrics: add stream api for system info

dashboard/src/models/SystemModel.js

@@ -94,6 +94,9 @@ function create() {
       if (error || result.status !== 200) return [error || result];
       return [null, result.body];
     },
+    async getMetricStream() {
+      return new EventSource(`${API_ORIGIN}/api/v1/system/metricstream?access_token=${accessToken}`);
+    }
   };
 }