Long stack traces do not display correctly

[jamakal]

When a very long stack trace is generated, it looks like the message that is sent to Slack is truncated. This means that the message sent to slack loses the 'end of code' termination, causing messages to be incorrectly formatted (three backticks displayed, message is not enclosed in a code block correctly) :

Can be reproduced with:

        Exception exception = new RuntimeException();
        for (int i = 0; i < 20; i++) {
            exception.addSuppressed(new RuntimeException());
        }
        LOGGER.error("Long exception", exception);