TUN-3777: Fix /ready endpoint for classic tunnels

Classic tunnels flow was triggering an event for RegisteringTunnel for
every connection that was about to be established, and then a Connected
event for every connection established.

However, the RegistreringTunnel event had no connection ID, always
causing it to unset/disconnect the 0th connection making the /ready
endpoint report incorrect numbers for classic tunnels.

cmd/cloudflared/ui/launch_ui.go

@@ -135,7 +135,7 @@ func (data *uiModel) Launch(
 			data.edgeURL = event.URL
 		case connection.RegisteringTunnel:
 			if data.edgeURL == "" {
-				tunnelHostText.SetText("Registering tunnel...")
+				tunnelHostText.SetText(fmt.Sprintf("Registering tunnel connection %d...", event.Index))
 			}
 		}
 		app.Draw()