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?
{
#if USE_BASE64 && USE_SSL && USE_INTERNAL_SSL_LIBRARY
    auto process = ShellCommand::execute(key_command);
    std::string b64_key;
    readStringUntilEOF(b64_key, process->out);
    process->wait();
    
    
    std::erase_if(b64_key, [](char c)
    {
        return c == ' ' || c == '\t' || c == '\r' || c == '\n';
    });
    std::vector<char> buf(b64_key.size());
    const size_t key_size = tb64dec(reinterpret_cast<const unsigned char *>(b64_key.data()), b64_key.size(),
                                    reinterpret_cast<unsigned char *>(buf.data()));
    if (!key_size)
        throw Exception("Failed to decode encryption key", ErrorCodes::INCORRECT_DATA);
    else if (key_size < 16)
        LOG_WARNING(log, "The encryption key should be at least 16 octets long.");
    const std::string_view key = std::string_view(buf.data(), key_size);
    CompressionCodecEncrypted::setMasterKey(key);
#else
    LOG_WARNING(log, "Server was built without Base64 or SSL support. Encryption is disabled.");
#endif
}
[[noreturn]] void forceShutdown()