**Describe the solution you'd like**

An option to make the `IDENTIFIED WITH` section mandatory.

const Poco::Util::AbstractConfiguration & config,
    const String & config_path,
    const zkutil::GetZooKeeper & get_zookeeper_function)
{
    String config_dir = std::filesystem::path{config_path}.remove_filename().string();
    String dbms_dir = config.getString("path", DBMS_DEFAULT_PATH);
    String include_from_path = config.getString("include_from", "/etc/metrika.xml");
    bool has_user_directories = config.has("user_directories");
    
    
    String users_config_path = config.getString("users_config", "");
    if (users_config_path.empty())