**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
from abc import ABCMeta, abstractmethod
from datetime import datetime, timedelta
from inspect import signature
from typing import (
    TYPE_CHECKING,
    Any,
    Callable,
    ClassVar,
    Dict,
    FrozenSet,
    Iterable,
    List,
    Optional,
    Sequence,
    Set,
    Tuple,
    Type,
    TypeVar,
    Union,
    cast,
)
import attr
import jinja2
from dateutil.relativedelta import relativedelta
from sqlalchemy.orm import Session
from sqlalchemy.orm.exc import NoResultFound
import airflow.templates
from airflow.compat.functools import cached_property
from airflow.configuration import conf
from airflow.exceptions import AirflowException, TaskDeferred