Allow RTT to be reported in prometheus:

• by src/dst namespace (default)
• by src/dst node
• by src/dst workload

If users need more metrics (such as by pod) they would be encouraged to use the Custom Metrics API instead (coming soon: NETOBSERV-1341 )

That will give the user the ability to set an alert on a specific value (100ms ?) and see the ribbon on network traffic page 

Also it will make RTT available without Loki install

These metrics will be available in prometheus, but at the moment without a dedicated chart in our dashboard (it would require more changes because our dashboard doesn't support histogram metrics at the moment)

Metric names are:

• netobserv_node_rtt_seconds
• netobserv_namespace_rtt_seconds
• netobserv_workload_rtt_seconds