wgsd: add package

wgsd: add package

Adds WGSD, a service that enables use cases such as:
- Building a mesh of WireGuard peers from a central registry
- Dynamic discovery of WireGuard Endpoint addressing (both IP address and port number)
- NAT-to-NAT WireGuard connectivity where UDP hole punching is supported.

Provides two packages:
- wgsd-coredns - a DNS-SD server, which allows clients to discover other
  wireguard peers
- wgsd-client - a client, which query DNS server and update wireguard
  peers endpoints

Signed-off-by: Vladimir Ermakov <redacted>