**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
render_template_as_native_obj: bool = False,
        tags: Optional[List[str]] = None,
    ):
        from airflow.utils.task_group import TaskGroup
        self.user_defined_macros = user_defined_macros
        self.user_defined_filters = user_defined_filters
        self.default_args = copy.deepcopy(default_args or {})
        self.params = params or {}
        
        if 'params' in self.default_args:
            self.params.update(self.default_args['params'])
            del self.default_args['params']
        validate_key(dag_id)
        self._dag_id = dag_id
        self._full_filepath = full_filepath if full_filepath else ''
        self._concurrency = concurrency
        self._pickle_id: Optional[int] = None
        self._description = description
        
        back = sys._getframe().f_back
        self.fileloc = back.f_code.co_filename if back else ""
        self.task_dict: Dict[str, BaseOperator] = {}
        
        if start_date and start_date.tzinfo:
            self.timezone = start_date.tzinfo
        elif 'start_date' in self.default_args and self.default_args['start_date']:
            if isinstance(self.default_args['start_date'], str):
                self.default_args['start_date'] = timezone.parse(self.default_args['start_date'])
            self.timezone = self.default_args['start_date'].tzinfo
        if not hasattr(self, 'timezone') or not self.timezone: