[haproxy-2] Frontend cache uses $backend variable

[matejzero]

In Cache / compressor section, all graphs for frontend metrics is using wrong label proxy=~$backend instead of proxy=~$frontend, so you get no data.

Examples:

• https://github.com/rfmoz/grafana-dashboards/blob/master/prometheus/haproxy-2-full.json#L6159
• https://github.com/rfmoz/grafana-dashboards/blob/master/prometheus/haproxy-2-full.json#L6172

I tried changing it to $frontend and it's working as intended.

[rfmoz]

Thanks for report the issue.