function truncateAggregateExceptions(exceptions, maxValueLength) {
  return exceptions.map(exception => {
    if (exception.value) {
      exception.value = string.truncate(exception.value, maxValueLength);
    }
    return exception;
  });
}
Truncate the message (exception.value) of all exceptions in the event.
Because this event processor is ran after `applyClientOptions`,
we need to truncate the message of the added exceptions here.