static String parentConfigId(String id) {
            if (id==null) return null;
            if (!id.contains("/")) return "";
            return id.substring(0, id.lastIndexOf('/'));
        }
The listing URL for this config in this service

@param key config key
@param rec recursive
@return url
configserver/src/main/java/com/yahoo/vespa/config/server/http/v2/HttpListConfigsHandler.java