Keep track of connections done for keep_alive HTTP probes.
Keep track of connections done for keep_alive HTTP probes.

If keep_alive is enabled, use net/http/httptrace to get notified when new connections are done. On ConnectDone, update a new counter "connect_event" and log when connection takes place.

With this we'll see new connections in logs like this:
"Established a new connection to: 172.217.9.164:80"

PiperOrigin-RevId: 318599259

google/cloudprober,google/cloudprober,cloudprober/cloudprober,cloudprober/cloudprober,cloudprober/cloudprober