**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

tests/core/test_configuration.py
#
#
#
import io
import os
import re
import tempfile
import textwrap
import unittest
import warnings
from collections import OrderedDict
from unittest import mock
import pytest
from airflow import configuration
from airflow.configuration import (
    AirflowConfigException,
    AirflowConfigParser,
    conf,
    expand_env_var,
    get_airflow_config,
    get_airflow_home,
    parameterized_config,
    run_command,
)