**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/models/test_baseoperator.py
"""Test render_template when a nested template field is missing."""
        task = BaseOperator(task_id="op1")
        with pytest.raises(AttributeError) as ctx:
            task.render_template(ClassWithCustomAttributes(template_fields=["missing_field"]), {})
        assert "'ClassWithCustomAttributes' object has no attribute 'missing_field'" == str(ctx.value)
    def test_jinja_invalid_expression_is_just_propagated(self):
        """Test render_template propagates Jinja invalid expression errors."""
        task = BaseOperator(task_id="op1")
        with pytest.raises(jinja2.exceptions.TemplateSyntaxError):
            task.render_template("{{ invalid expression }}", {})
    @mock.patch("airflow.templates.SandboxedEnvironment", autospec=True)
    def test_jinja_env_creation(self, mock_jinja_env):
        """Verify if a Jinja environment is created only once when templating."""
        task = MockOperator(task_id="op1", arg1="{{ foo }}", arg2="{{ bar }}")
        task.render_template_fields(context={"foo": "whatever", "bar": "whatever"})
        assert mock_jinja_env.call_count == 1
    def test_default_resources(self):
        task = BaseOperator(task_id="default-resources")
        assert task.resources is None
    def test_custom_resources(self):
        task = BaseOperator(task_id="custom-resources", resources={"cpus": 1, "ram": 1024})
        assert task.resources.cpus.qty == 1
        assert task.resources.ram.qty == 1024
    def test_default_email_on_actions(self):
        test_task = BaseOperator(task_id='test_default_email_on_actions')
        assert test_task.email_on_retry is True
        assert test_task.email_on_failure is True
    def test_email_on_actions(self):