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?
#include "Keeper.h"
#include <sys/stat.h>
#include <pwd.h>
#include <Common/ClickHouseRevision.h>
#include <Server/ProtocolServerAdapter.h>
#include <Common/DNSResolver.h>
#include <Interpreters/DNSCacheUpdater.h>
#include <Poco/Net/NetException.h>
#include <Poco/Net/TCPServerParams.h>
#include <Poco/Net/TCPServer.h>
#include <common/defines.h>
#include <common/logger_useful.h>
#include <common/ErrorHandlers.h>
#include <common/scope_guard.h>
#include <Poco/Util/HelpFormatter.h>
#include <Poco/Version.h>
#include <Poco/Environment.h>
#include <Common/getMultipleKeysFromConfig.h>
#include <filesystem>
#include <IO/UseSSL.h>
#if !defined(ARCADIA_BUILD)
#   include "config_core.h"
#   include "Common/config_version.h"
#endif
#if USE_SSL
#    include <Poco/Net/Context.h>
#    include <Poco/Net/SecureServerSocket.h>
#endif
#include <Server/KeeperTCPHandlerFactory.h>
#if defined(OS_LINUX)