Allow DNS (latency & response codes) to be reported in prometheus.

That will give the user the ability to set an alert on a specific value and see the ribbon on network traffic page 

Also it will make DNS available without Loki install

Add related metrics to the dashboards - this implies implementing histograms in dashboards (e.g. p99 / p50), which now allows to have the RTT metrics in dashboard (which wasn't done via NETOBSERV-1231)