**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
option = self._get_cmd_option(section, key)
        if option:
            return option
        if deprecated_section:
            option = self._get_cmd_option(deprecated_section, deprecated_key)
            if option:
                self._warn_deprecate(section, key, deprecated_section, deprecated_key)
                return option
        return None
    def _get_option_from_config_file(self, deprecated_key, deprecated_section, key, kwargs, section):
        
        if super().has_option(section, key):
            
            
            return expand_env_var(super().get(section, key, **kwargs))
        if deprecated_section:
            if super().has_option(deprecated_section, deprecated_key):
                self._warn_deprecate(section, key, deprecated_section, deprecated_key)
                return expand_env_var(super().get(deprecated_section, deprecated_key, **kwargs))
        return None
    def _get_environment_variables(self, deprecated_key, deprecated_section, key, section):