**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
test_config = '''
[kubernetes_environment_variables]
key1 = hello
AIRFLOW_HOME = /root/airflow
'''
        test_config_default = '''
[kubernetes_environment_variables]
'''
        test_conf = AirflowConfigParser(default_config=parameterized_config(test_config_default))
        test_conf.read_string(test_config)
        assert OrderedDict([('key1', 'hello'), ('AIRFLOW_HOME', '/root/airflow')]) == test_conf.getsection(
            'kubernetes_environment_variables'
        )
    def test_broker_transport_options(self):
        section_dict = conf.getsection("celery_broker_transport_options")
        assert isinstance(section_dict['visibility_timeout'], int)
        assert isinstance(section_dict['_test_only_bool'], bool)
        assert isinstance(section_dict['_test_only_float'], float)
        assert isinstance(section_dict['_test_only_string'], str)
    @conf_vars(
        {
            ("celery", "worker_concurrency"): None,
            ("celery", "celeryd_concurrency"): None,
        }
    )
    def test_deprecated_options(self):