Publish the grafana dashboard for the tracker stats

[josecelano]

Relates to: #20

I can't publish the Grafana dashboard for the Live Demo Tracker stats.

The URL for the public dashboard: http://grafana.torrust-demo.com:3100/public-dashboards/21e9561260e047b48a8c0a09d1b68ded

I had a warning trying to publish it because it seems dashboards with Template Variables are not supported.

Prometheus is a supported data source:

https://grafana.com/docs/grafana/latest/dashboards/dashboard-public/#supported-data-sources

But there are some limitations:

https://grafana.com/docs/grafana/latest/dashboards/dashboard-public/#limitations

I think the problem could be:

• Template variables are not supported, and it seems I'm using them (auto).
• Or Prometheus is only accessible in the backend docker network by grafana but not publicly.

This is not a high priority since we are planning to use the dashboard internally:

• To check the performance impact of some changes.
• To help to find the reason for some bugs.
• To detect errors early after deployments.

How the dashboard looks like now when you are authenticated user:

[josecelano]

I've enabled Grafana via Ngxin proxy on https://grafana.torrust-demo.com/ and I have the same problem. I see no data in the dashboard even when I'm logged in. It seems it's using websockets.