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?
const Poco::Util::AbstractConfiguration & config,
    const std::string & config_path,
    const std::string & users_config_path,
    Poco::Logger * log)
{
    if (config.getBool("skip_check_for_incorrect_settings", false))
        return;
    if (config.has("users") || config.has("profiles") || config.has("quotas"))
    {
        
        
        LOG_ERROR(log, "The <users>, <profiles> and <quotas> elements should be located in users config file: {} not in main config {}."
            " Also note that you should place configuration changes to the appropriate *.d directory like 'users.d'.",
            users_config_path, config_path);
    }
}
static void loadEncryptionKey(const std::string & key_command [[maybe_unused]], Poco::Logger * log)