Add an opt-in nmstate network engine via `network_engine: nmstate` for host network configuration using NetworkManager/libnmstate. Implement nmstate rendering for Ethernet, VLAN, bond, bridge, routes, routing rules, and structured `*_ethtool_config`. Add OVS patch link (veth pair) generation in nmstate rendering. Change-Id: If3a92b059063b0aea299a51e76217c0d90a637a5 Assisted-by: various models Signed-off-by: Grzegorz Koper <grzegorzk@stackhpc.com>