Zonal network endpoint groups (NEGs) with GCE_VM_IP and GCE_VM_IP_PORT

## Feature Feature Zonal network endpoint groups (NEGs) with `GCE_VM_IP` and `GCE_VM_IP_PORT`endpoints support IPv6-only endpoints that reference IPv6-only or dual-stack Compute Engine VM network interfaces. This feature is available in **Preview**. For more information, see [Zonal network endpoint groups overview](https://cloud.google.com/load-balancing/docs/negs/zonal-neg-concepts).