e2e tests need a ping6 test for IPv6-only clusters

e2e tests provide only an (IPv4) ping test for external connectivity.

We need a way to conditionally run a ping6 external connectivity check,
and disable the (IPv4) ping-based external connectivity check,
for end-to-end testing on IPv6-only clusters.

This feature will be needed for creating gating IPv6 CI tests.

fixes #53383

test/e2e/framework/util.go

@@ -4503,15 +4503,22 @@ func LaunchWebserverPod(f *Framework, podName, nodeName string) (ip string) {
 	return
 }
 
+type PingCommand string
+
+const (
+	IPv4PingCommand PingCommand = "ping"
+	IPv6PingCommand PingCommand = "ping6"
+)
+
 // CheckConnectivityToHost launches a pod to test connectivity to the specified
 // host. An error will be returned if the host is not reachable from the pod.
 //
 // An empty nodeName will use the schedule to choose where the pod is executed.
-func CheckConnectivityToHost(f *Framework, nodeName, podName, host string, timeout int) error {
+func CheckConnectivityToHost(f *Framework, nodeName, podName, host string, pingCmd PingCommand, timeout int) error {
 	contName := fmt.Sprintf("%s-container", podName)
 
 	command := []string{
-		"ping",
+		string(pingCmd),
 		"-c", "3", // send 3 pings
 		"-W", "2", // wait at most 2 seconds for a reply
 		"-w", strconv.Itoa(timeout),