I couldn't find any official documentation specifying what each parameter to a `sla_miss_callback` callable are. This would be a great addition to know how to properly format the messages sent.
airflow/models/dag.py
warnings.warn(
            "`DAG.normalize_schedule()` is deprecated.",
            category=DeprecationWarning,
            stacklevel=2,
        )
        with warnings.catch_warnings():
            warnings.simplefilter("ignore", DeprecationWarning)
            following = self.following_schedule(dttm)
        if not following:  
            return dttm
        with warnings.catch_warnings():
            warnings.simplefilter("ignore", DeprecationWarning)
            previous_of_following = self.previous_schedule(following)
        if previous_of_following != dttm:
            return following
        return dttm
    @provide_session
    def get_last_dagrun(self, session=None, include_externally_triggered=False):