**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/configuration.py
return _deprecated[name]()
    raise AttributeError(f"module {__name__} has no attribute {name}")
AIRFLOW_HOME = get_airflow_home()
AIRFLOW_CONFIG = get_airflow_config(AIRFLOW_HOME)
_TEST_DAGS_FOLDER = os.path.join(
    os.path.dirname(os.path.dirname(os.path.realpath(__file__))), 'tests', 'dags'
)
if os.path.exists(_TEST_DAGS_FOLDER):
    TEST_DAGS_FOLDER = _TEST_DAGS_FOLDER
else:
    TEST_DAGS_FOLDER = os.path.join(AIRFLOW_HOME, 'dags')
_TEST_PLUGINS_FOLDER = os.path.join(
    os.path.dirname(os.path.dirname(os.path.realpath(__file__))), 'tests', 'plugins'
)
if os.path.exists(_TEST_PLUGINS_FOLDER):
    TEST_PLUGINS_FOLDER = _TEST_PLUGINS_FOLDER
else:
    TEST_PLUGINS_FOLDER = os.path.join(AIRFLOW_HOME, 'plugins')
TEST_CONFIG_FILE = get_airflow_test_config(AIRFLOW_HOME)
SECRET_KEY = b64encode(os.urandom(16)).decode('utf-8')
FERNET_KEY = ''  
WEBSERVER_CONFIG = ''  
conf = initialize_config()
secrets_backend_list = initialize_secrets_backends()
conf.validate()
PY37 = sys.version_info >= (3, 7)
if not PY37:
    from pep562 import Pep562
    Pep562(__name__)