The PoC of this solution must:

• update the UDN / C-UDN API to have a new "gateway" attribute
  • when omitted, the gateway shall be the current hard-coded value - the first IP in the UDN's subnet
  • the OVN-K CNI NetConf object must be updated with this information
• create a VM attached to a primary UDN with IPAM, with a specified gateway
  • the guest must be configured with this gateway, using RAs for IPv6 or DHCP offers for IPv4
• the gateway routers on each worker node must be configured properly with this gateway address
• the VM must be able to egress from the overlay network to the internet
• a load-balancer / node port / cluster IP service must be able to ingress into the VM when the gateway is overridden

This PoC (should) only require changes to OVN-Kubernetes.