public Optional<ServiceReference> service() {
        return Optional.ofNullable(this.service);
    }
@return `service` is a reference to the service for this webhook. Either `service` or `url` must be specified.

If the webhook is running within the cluster, then you should use `service`.
sdk/java/src/main/java/com/pulumi/kubernetes/admissionregistration/v1beta1/outputs/WebhookClientConfig.java