prom: add prom2 dashboard as bundled dashboard

public/app/plugins/datasource/prometheus/plugin.json

@@ -5,6 +5,7 @@
 
   "includes": [
     {"type": "dashboard", "name": "Prometheus Stats", "path": "dashboards/prometheus_stats.json"},
+    {"type": "dashboard", "name": "Prometheus 2.0 Stats", "path": "dashboards/prometheus_2_stats.json"},
     {"type": "dashboard", "name": "Grafana Stats", "path": "dashboards/grafana_stats.json"}
   ],