**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
dag_run = (
                    session.query(DagRun)
                    .filter(
                        DagRun.dag_id == self.dag_id,
                        DagRun.execution_date == info.logical_date,
                    )
                    .one()
                )
                ti = TaskInstance(self, run_id=dag_run.run_id)
            except NoResultFound:
                
                dr = DagRun(
                    dag_id=self.dag_id,
                    run_id=DagRun.generate_run_id(DagRunType.MANUAL, info.logical_date),
                    run_type=DagRunType.MANUAL,
                    execution_date=info.logical_date,
                    data_interval=info.data_interval,
                )
                ti = TaskInstance(self, run_id=None)
                ti.dag_run = dr
                session.add(dr)
                session.flush()
            ti.run(
                mark_success=mark_success,
                ignore_depends_on_past=ignore_depends_on_past,
                ignore_ti_state=ignore_ti_state,
                test_mode=test_mode,
                session=session,
            )
    def dry_run(self) -> None: