I’m deploying a Kubernetes Gateway in Google Kubernetes Engine. How can I get the external IP to expose it as an output?

resource "kubernetes_manifest" "gateway" {
  manifest = {
    "apiVersion" = "gateway.networking.k8s.io/v1beta1"
    "kind"       = "Gateway"
    "metadata" = {
      "namespace" = "default"
      "name"      = "my-gateway"
    }
    "spec" = {
      "gatewayClassName" = "gke-l7-regional-external-managed" // Managed by GKE
      "listeners" = [
        {
          "name"     = "http"
          "protocol" = "HTTP"
          "port"     = 80
          "allowedRoutes" = {
            "namespaces" = {
              "from" : "All"
            }
            "kinds" = [{
              "kind" = "HTTPRoute"
            }]
          }
        }
      ]
    }
  }
}

When I run kubectl get gateways, I can see the public IP.

output "gateway_external_ip" {
  value = kubernetes_manifest.gateway. // what goes here?
}

I have exported the whole resource but I don’t see how to fetch the IP. Is it even possible?