IMessageFormatter param is not nullable

[onatsko]

I use your lib for sending message to Telegram, it works great, thank you!

But today I enable nullable in project
and get error on code:

   logConfig = logConfig.WriteTo.Telegram(config => { ....  }, null, logLevelError);

null is param IMessageFormatter messageFormatter

in ctor I see that it is not nullable

    public static LoggerConfiguration Telegram(
      this LoggerSinkConfiguration loggerConfiguration,
      Action<TelegramSinkConfiguration> configureAction,
      IMessageFormatter messageFormatter,
      LogEventLevel restrictedToMinimumLevel = LogEventLevel.Verbose)

but in next ctor TelegramSink is nullable

    public TelegramSink(
      ChannelWriter<LogEvent> channelWriter,
      ILogsQueueAccessor logsQueueAccessor,
      TelegramSinkConfiguration sinkConfiguration,
      IMessageFormatter? messageFormatter)

pls make IMessageFormatter nullable in LoggerConfiguration Telegram

[Bardin08]

Fixed #38