**Description**

It would be nice if the weight_rule default value could be managed by a global config

suggested config:
```
# Weighting method used for the effective total priority weight of the task. 
# Options are: { downstream | upstream | absolute } default is
default_weight_rule = downstream
```
**Use case / motivation**

In some pipeline, you really need to have absolute weight, and then you have to add a line in each task definition which is annoying

airflow/models/baseoperator.py
context: Any,
        task_ids: Optional[List[str]] = None,
        dag_id: Optional[str] = None,
        key: str = XCOM_RETURN_KEY,
        include_prior_dates: Optional[bool] = None,
    ) -> Any:
        """
        Pull XComs that optionally meet certain criteria.
        The default value for `key` limits the search to XComs