**Description**

In similar fashion to https://github.com/apache/airflow/pull/4083, it would be helpful for Airflow to reattach itself to the ECS Task rather than letting another instance to start. However, instead of making this the default behavior, it would be better to use a `reattach` flag.

**Use case / motivation**

Allow Airflow the option to reattach to an existing ECS task when a restart happens, which would avoid having "rogue" tasks.
airflow/providers/amazon/aws/operators/ecs.py
"""https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/ecs.html#ECS.Client.describe_tasks"""  
        ...
    def stop_task(self, cluster, task, reason: str) -> dict:
        """https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/ecs.html#ECS.Client.stop_task"""  
        ...
class ECSOperator(BaseOperator):  
    """
    Execute a task on AWS ECS (Elastic Container Service)
    .. seealso::
        For more information on how to use this operator, take a look at the guide:
        :ref:`howto/operator:ECSOperator`
    :param task_definition: the task definition name on Elastic Container Service
    :type task_definition: str
    :param cluster: the cluster name on Elastic Container Service
    :type cluster: str
    :param overrides: the same parameter that boto3 will receive (templated):
        https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/ecs.html#ECS.Client.run_task
    :type overrides: dict
    :param aws_conn_id: connection id of AWS credentials / region name. If None,
        credential boto3 strategy will be used
        (http://boto3.readthedocs.io/en/latest/guide/configuration.html).
    :type aws_conn_id: str
    :param region_name: region name to use in AWS Hook.
        Override the region_name in connection (if provided)
    :type region_name: str
    :param launch_type: the launch type on which to run your task ('EC2' or 'FARGATE')
    :type launch_type: str
    :param group: the name of the task group associated with the task
    :type group: str