**Description**

For a DAG that looks like this:

```
A >> B
```

If A fails, B goes into "upstream_failed" state. If a user then marks A "success", B will remain in "upstream_failed" state. It will not automatically start running. This scenario often happens if the failure of A is dealt with outside of Airflow and the user does not want Airflow to run A again. But he usually expect Airflow to run B after A is marked "success".

**Use case / motivation**

After A is marked "success", its downstream tasks B should be cleared automatically and get ready to be scheduled. To avoid changing this behaviour completely, there can be a toggle button next to "Success" that lets the user decide if he wants Airflow to automatically clear downstream tasks that are in "upstream_failed" state.
airflow/models/dag.py
only_running=only_running,
                    confirm_prompt=confirm_prompt,
                    include_subdags=include_subdags,
                    include_parentdag=False,
                    dag_run_state=dag_run_state,
                    get_tis=True,
                    session=session,
                    recursion_depth=recursion_depth,
                    max_recursion_depth=max_recursion_depth,
                    dag_bag=dag_bag,
                    visited_external_tis=visited_external_tis,
                )
            )
        if start_date:
            tis = tis.filter(TI.execution_date >= start_date)
        if end_date:
            tis = tis.filter(TI.execution_date <= end_date)
        if only_failed:
            tis = tis.filter(or_(TI.state == State.FAILED, TI.state == State.UPSTREAM_FAILED))
        if only_running:
            tis = tis.filter(TI.state == State.RUNNING)
        if task_ids:
            tis = tis.filter(TI.task_id.in_(task_ids))
        if include_subdags:
            from airflow.sensors.external_task import ExternalTaskMarker
            
            instances = tis.all()
            for ti in instances:
                if ti.operator == ExternalTaskMarker.__name__:
                    if visited_external_tis is None: