terraform/gcp: Add ingress_whitelist (#8590)

Also, do not create unneeded resources (target pools are charged and should
only be created when needed).

contrib/terraform/gcp/main.tf

@@ -33,4 +33,5 @@ module "kubernetes" {
   ssh_whitelist        = var.ssh_whitelist
   api_server_whitelist = var.api_server_whitelist
   nodeport_whitelist   = var.nodeport_whitelist
+  ingress_whitelist    = var.ingress_whitelist
 }