fix: allow transfer for external-dns (#456)

external-dns required axfr support to remove old records. add the
capability for the externaldns tsig key.

Reviewed-on: #456

modules/externaldns/manifests/master.pp

@@ -28,8 +28,8 @@ class externaldns::master inherits externaldns {
       dynamic         => true,
       allow_updates   => ['key externaldns-key'],
       allow_transfers => empty($slave_ips) ? {
-        true  => [],
-        false => ['dns-slaves'],
+        true  => ['key externaldns-key'],
+        false => ['key externaldns-key','dns-slaves'],
       },
       ns_notify       => !empty($slave_ips),
       also_notify     => $slave_ips,