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/verbena/configuration.nix

@@ -2,8 +2,6 @@
 {
   imports = [
     self.nixosModules.nix-defaults
-    ../../modules/unbound.nix
-    ../../modules/unbound-auth.nix
     self.nixosModules.nextcloud
     self.nixosModules.gitea