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
"""
        Returns the number of active "running" dag runs
        :param external_trigger: True for externally triggered active dag runs
        :type external_trigger: bool
        :param session:
        :return: number greater than 0 for active dag runs
        """
        
        query = (
            session.query(func.count())
            .filter(DagRun.dag_id == self.dag_id)
            .filter(DagRun.state == State.RUNNING)
        )
        if external_trigger is not None:
            query = query.filter(
                DagRun.external_trigger == (expression.true() if external_trigger else expression.false())
            )
        return query.scalar()
    @provide_session
    def get_dagrun(