clan: migrate internal DNS to coredns service

Currently using a patched version of the upstream
coredns service, with hard-coded IPs until
wireguard exports are supported.

Zerotier connections were flaky and wireguard
seems more stable (although it seems to have a bit
less throughput).

machines/genepi/configuration.nix

@@ -20,8 +20,6 @@
 
     ../../modules/acme-home.nix
     ../../modules/lounge.nix
-    ../../modules/unbound.nix
-    ../../modules/unbound-auth.nix
     self.nixosModules.nix-defaults
 
     self.nixosModules.user-rpqt