time to establish connection (libp2p#3134)

Implementing libp2p#2745 , adding  a metric to break down time from connection pending to connection established, per protocol stack.

````
$curl -s http://127.0.0.1:42183/metrics | grep nt_duration
# HELP libp2p_swarm_connection_establishment_duration Time it took (locally) to finish establishing connections.
# TYPE libp2p_swarm_connection_establishment_duration histogram
libp2p_swarm_connection_establishment_duration_sum{role="Listener",protocols="/ip4/tcp"} 0.007
libp2p_swarm_connection_establishment_duration_count{role="Listener",protocols="/ip4/tcp"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Listener",protocols="/ip4/tcp",le="0.001"} 0
libp2p_swarm_connection_establishment_duration_bucket{role="Listener",protocols="/ip4/tcp",le="0.002"} 0
libp2p_swarm_connection_establishment_duration_bucket{role="Listener",protocols="/ip4/tcp",le="0.004"} 0
libp2p_swarm_connection_establishment_duration_bucket{role="Listener",protocols="/ip4/tcp",le="0.008"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Listener",protocols="/ip4/tcp",le="0.016"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Listener",protocols="/ip4/tcp",le="0.032"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Listener",protocols="/ip4/tcp",le="0.064"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Listener",protocols="/ip4/tcp",le="0.128"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Listener",protocols="/ip4/tcp",le="0.256"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Listener",protocols="/ip4/tcp",le="0.512"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Listener",protocols="/ip4/tcp",le="+Inf"} 1

lbl@chomp:~lbl
$curl -s http://127.0.0.1:34283/metrics | grep nt_duration
# HELP libp2p_swarm_connection_establishment_duration Time it took (locally) to finish establishing connections.
# TYPE libp2p_swarm_connection_establishment_duration histogram
libp2p_swarm_connection_establishment_duration_sum{role="Dialer",protocols="/ip4/tcp"} 0.009
libp2p_swarm_connection_establishment_duration_count{role="Dialer",protocols="/ip4/tcp"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Dialer",protocols="/ip4/tcp",le="0.001"} 0
libp2p_swarm_connection_establishment_duration_bucket{role="Dialer",protocols="/ip4/tcp",le="0.002"} 0
libp2p_swarm_connection_establishment_duration_bucket{role="Dialer",protocols="/ip4/tcp",le="0.004"} 0
libp2p_swarm_connection_establishment_duration_bucket{role="Dialer",protocols="/ip4/tcp",le="0.008"} 0
libp2p_swarm_connection_establishment_duration_bucket{role="Dialer",protocols="/ip4/tcp",le="0.016"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Dialer",protocols="/ip4/tcp",le="0.032"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Dialer",protocols="/ip4/tcp",le="0.064"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Dialer",protocols="/ip4/tcp",le="0.128"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Dialer",protocols="/ip4/tcp",le="0.256"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Dialer",protocols="/ip4/tcp",le="0.512"} 1
libp2p_swarm_connection_establishment_duration_bucket{role="Dialer",protocols="/ip4/tcp",le="+Inf"} 1
````

tests/test_server.rs

@@ -195,6 +195,7 @@ async fn test_dial_back() {
                         },
                     num_established,
                     concurrent_dial_errors,
+                    established_in: _,
                 } => {
                     assert_eq!(peer_id, client_id);
                     assert_eq!(num_established, NonZeroU32::new(2).unwrap());