**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
('logging', 'colored_log_format'): ('core', 'colored_log_format', '2.0.0'),
        ('logging', 'colored_formatter_class'): ('core', 'colored_formatter_class', '2.0.0'),
        ('logging', 'log_format'): ('core', 'log_format', '2.0.0'),
        ('logging', 'simple_log_format'): ('core', 'simple_log_format', '2.0.0'),
        ('logging', 'task_log_prefix_template'): ('core', 'task_log_prefix_template', '2.0.0'),
        ('logging', 'log_filename_template'): ('core', 'log_filename_template', '2.0.0'),
        ('logging', 'log_processor_filename_template'): ('core', 'log_processor_filename_template', '2.0.0'),
        ('logging', 'dag_processor_manager_log_location'): (
            'core',
            'dag_processor_manager_log_location',
            '2.0.0',
        ),
        ('logging', 'task_log_reader'): ('core', 'task_log_reader', '2.0.0'),
        ('metrics', 'statsd_on'): ('scheduler', 'statsd_on', '2.0.0'),
        ('metrics', 'statsd_host'): ('scheduler', 'statsd_host', '2.0.0'),
        ('metrics', 'statsd_port'): ('scheduler', 'statsd_port', '2.0.0'),
        ('metrics', 'statsd_prefix'): ('scheduler', 'statsd_prefix', '2.0.0'),
        ('metrics', 'statsd_allow_list'): ('scheduler', 'statsd_allow_list', '2.0.0'),
        ('metrics', 'stat_name_handler'): ('scheduler', 'stat_name_handler', '2.0.0'),
        ('metrics', 'statsd_datadog_enabled'): ('scheduler', 'statsd_datadog_enabled', '2.0.0'),
        ('metrics', 'statsd_datadog_tags'): ('scheduler', 'statsd_datadog_tags', '2.0.0'),
        ('metrics', 'statsd_custom_client_path'): ('scheduler', 'statsd_custom_client_path', '2.0.0'),
        ('scheduler', 'parsing_processes'): ('scheduler', 'max_threads', '1.10.14'),
        ('operators', 'default_queue'): ('celery', 'default_queue', '2.1.0'),
        ('core', 'hide_sensitive_var_conn_fields'): ('admin', 'hide_sensitive_variable_fields', '2.1.0'),
        ('core', 'sensitive_var_conn_names'): ('admin', 'sensitive_variable_fields', '2.1.0'),
        ('core', 'default_pool_task_slot_count'): ('core', 'non_pooled_task_slot_count', '1.10.4'),
        ('core', 'max_active_tasks_per_dag'): ('core', 'dag_concurrency', '2.2.0'),
        ('logging', 'worker_log_server_port'): ('celery', 'worker_log_server_port', '2.2.0'),
        ('api', 'access_control_allow_origins'): ('api', 'access_control_allow_origin', '2.2.0'),