nixos/pdns-recursor: configure as local resolver (#417015)

nixos/modules/services/networking/pdns-recursor.nix

···
 
     environment.etc."/pdns-recursor/recursor.yml".source = configFile;
 
+    networking.resolvconf.useLocalResolver = lib.mkDefault true;
+
     services.pdns-recursor.yaml-settings = {
       incoming = mkDefaultAttrs {
         listen = cfg.dns.address;