**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/models/baseoperator.py
r"""
    Given a number of tasks, builds a dependency chain.
    This function accepts values of BaseOperator (aka tasks), EdgeModifiers (aka Labels), XComArg, TaskGroups,
    or lists containing any mix of these types (or a mix in the same list). If you want to chain between two
    lists you must ensure they have the same length.
    Using classic operators/sensors:
    .. code-block:: python
        chain(t1, [t2, t3], [t4, t5], t6)
    is equivalent to::
          / -> t2 -> t4 \
        t1               -> t6
          \ -> t3 -> t5 /
    .. code-block:: python
        t1.set_downstream(t2)
        t1.set_downstream(t3)
        t2.set_downstream(t4)