**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
path = _default_config_file_path('default_airflow.cfg')
    with open(path) as fh:
        return fh.read()
@functools.lru_cache(maxsize=None)
def _TEST_CONFIG():
    path = _default_config_file_path('default_test.cfg')
    with open(path) as fh:
        return fh.read()
_deprecated = {
    'DEFAULT_CONFIG': _DEFAULT_CONFIG,
    'TEST_CONFIG': _TEST_CONFIG,
    'TEST_CONFIG_FILE_PATH': functools.partial(_default_config_file_path, ('default_test.cfg')),
    'DEFAULT_CONFIG_FILE_PATH': functools.partial(_default_config_file_path, ('default_airflow.cfg')),
}
def __getattr__(name):
    if name in _deprecated:
        warnings.warn(
            f"{__name__}.{name} is deprecated and will be removed in future",
            DeprecationWarning,
            stacklevel=2,
        )