feat(swarm): expose ConnectionId and add conn duration metric

- Exposes the `ConnectionId` in the various `SwarmEvent` variants.
- Tracks connection duration in `libp2p-metrics::swarm`.

Pull-Request: #3927.

examples/dcutr/src/main.rs

@@ -267,7 +267,7 @@ fn main() -> Result<(), Box<dyn Error>> {
                 } => {
                     info!("Established connection to {:?} via {:?}", peer_id, endpoint);
                 }
-                SwarmEvent::OutgoingConnectionError { peer_id, error } => {
+                SwarmEvent::OutgoingConnectionError { peer_id, error, .. } => {
                     info!("Outgoing connection error to {:?}: {:?}", peer_id, error);
                 }
                 _ => {}