**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
"""
        Reads options, imports the full qualified name, and returns the object.
        In case of failure, it throws an exception with the key and section names
        :return: The object or None, if the option is empty
        """
        full_qualified_path = conf.get(section=section, key=key, **kwargs)
        if not full_qualified_path:
            return None
        try:
            return import_string(full_qualified_path)
        except ImportError as e:
            log.error(e)
            raise AirflowConfigException(
                f'The object could not be loaded. Please check "{key}" key in "{section}" section. '
                f'Current value: "{full_qualified_path}".'
            )
    def read(self, filenames, encoding=None):
        super().read(filenames=filenames, encoding=encoding)
    def read_dict(self, dictionary, source='<dict>'):
        super().read_dict(dictionary=dictionary, source=source)
    def has_option(self, section, option):
        try:
            
            
            
            self.get(section, option, fallback=_UNSET)
            return True
        except (NoOptionError, NoSectionError):
            return False
    def remove_option(self, section, option, remove_default=True):