Write a file `uuid` in server's data directory that contains random UUID, generated at startup if file does not exist.

It will be used for several purposes:
- to anonymously identify server in Sentry (currently Sentry is unusable);
- (possible future usage) to identify server in ensemble.

@tavplubix comments?
{
    logger().information("shutting down");
    BaseDaemon::uninitialize();
}
int Keeper::run()
{
    if (config().hasOption("help"))
    {
        Poco::Util::HelpFormatter help_formatter(Keeper::options());
        auto header_str = fmt::format("{} [OPTION] [-- [ARG]...]\n"
                                      "positional arguments can be used to rewrite config.xml properties, for example, --http_port=8010",
                                      commandName());
        help_formatter.setHeader(header_str);
        help_formatter.format(std::cout);
        return 0;
    }
    if (config().hasOption("version"))
    {
        std::cout << DBMS_NAME << " keeper version " << VERSION_STRING << VERSION_OFFICIAL << "." << std::endl;
        return 0;
    }
    return Application::run(); 
}
void Keeper::initialize(Poco::Util::Application & self)