Save answer event to log file.

def emit_answer_event(sender, instance, **kwargs):
    """
    Save answer event to log file.
    """
    if not issubclass(sender, Answer) or not kwargs['created']:
        return
    logger = get_events_logger()
    logger.emit('answer', {
        "user_id": instance.user_id,
        "is_correct": instance.item_asked_id == instance.item_answered_id,
        "context_id": [instance.context_id] if instance.context_id else [],
        "item_id": instance.item_id,
        "response_time_ms": instance.response_time,
        "params": {
            "session_id": instance.session_id,
            "guess": instance.guess,
            "practice_set_id": instance.practice_set_id,
            "config_id": instance.config_id,
        }}
    )