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?
{
    Poco::Logger * log = &logger();
    UseSSL use_ssl;
    MainThreadStatus::getInstance();
#if !defined(NDEBUG) || !defined(__OPTIMIZE__)
    LOG_WARNING(log, "Keeper was built in debug mode. It will work slowly.");
#endif
#if defined(SANITIZER)
    LOG_WARNING(log, "Keeper was built with sanitizer. It will work slowly.");
#endif
    auto shared_context = Context::createShared();
    global_context = Context::createGlobal(shared_context.get());
    global_context->makeGlobalContext();
    global_context->setApplicationType(Context::ApplicationType::KEEPER);
    if (!config().has("keeper_server"))
        throw Exception(ErrorCodes::NO_ELEMENTS_IN_CONFIG, "Keeper configuration (<keeper_server> section) not found in config");
    std::string path;
    if (config().has("keeper_server.storage_path"))
        path = config().getString("keeper_server.storage_path");
    else if (config().has("keeper_server.log_storage_path"))
        path = config().getString("keeper_server.log_storage_path");
    else if (config().has("keeper_server.snapshot_storage_path"))
        path = config().getString("keeper_server.snapshot_storage_path");
    else
        path = std::filesystem::path{KEEPER_DEFAULT_PATH};