**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
"""Stringified DAGs and operators contain exactly these fields."""
        if not cls.__serialized_fields:
            from airflow.models.dag import DagContext
            
            
            
            
            DagContext.push_context_managed_dag(None)
            cls.__serialized_fields = frozenset(
                vars(BaseOperator(task_id='test')).keys()
                - {
                    'inlets',
                    'outlets',
                    '_upstream_task_ids',
                    'default_args',
                    'dag',
                    '_dag',
                    '_BaseOperator__instantiated',
                }
                | {
                    '_task_type',
                    'subdag',
                    'ui_color',
                    'ui_fgcolor',
                    'template_ext',
                    'template_fields',
                    'template_fields_renderers',
                    'params',
                }