unetd: add WireGuard based VPN connection manager for OpenWrt

unetd: add WireGuard based VPN connection manager for OpenWrt

This package simplifies setting up wireguard networks on OpenWrt by a wireguard
network as a JSON file, which can be shared across all participating nodes.
It can be signed with an authentication key and automatically kept in sync.
unetd also supports deterministically generating ipv6 addresses for each host
based on the public key and storing those in a hosts file that can be used with
dnsmasq. It also supports automatically creating VXLAN tunnels between multiple
endpoints.

Signed-off-by: Felix Fietkau <nbd@nbd.name>