**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
for (section, key) in self.sensitive_config_values:
            opt = self._get_secret_option(section, key)
            if opt:
                if not display_sensitive:
                    opt = '< hidden >'
                if display_source:
                    opt = (opt, 'secret')
                elif raw:
                    opt = opt.replace('%', '%%')
                config_sources.setdefault(section, OrderedDict()).update({key: opt})
                del config_sources[section][key + '_secret']
    def _include_commands(self, config_sources, display_sensitive, display_source, raw):
        for (section, key) in self.sensitive_config_values:
            opt = self._get_cmd_option(section, key)
            if not opt:
                continue
            if not display_sensitive:
                opt = '< hidden >'
            if display_source:
                opt = (opt, 'cmd')
            elif raw:
                opt = opt.replace('%', '%%')
            config_sources.setdefault(section, OrderedDict()).update({key: opt})
            del config_sources[section][key + '_cmd']
    def _include_envs(self, config_sources, display_sensitive, display_source, raw):