[Helper] Add ejabberd to DNS overrides

helper-scripts/docker-compose.override.yml.d/EXTERNAL_DNS/docker-compose.override.yml

@@ -42,3 +42,7 @@ services:
     dockerapi-mailcow:
       dns:
         - my.resolvers.ip.addr
+
+    ejabberd-mailcow:
+      dns:
+        - my.resolvers.ip.addr