Add Grafana Dashboards

We should provide Grafana dashboards.

GitHub wish:

I recently went through the effort to add Prometheus and Grafana based monitoring to a search stack for ecommerce applications, and what made the experience really great was that there was already a wonderful Solr template and Rails template dashboards available from Grafana. Writing your own Grafana dashboard isn't for the faint of heart!

Would you be able to publish a template dashboard for Zeppelin as well? That would move this from a "hey, we should monitor Zeppelin" to a "no excuses, its easy to monitor Zeppelin"