**Description**

It would be great having a option to abort a DAG Runs through the REST API.

**Use case / motivation**

The proposed input params would be:
 - DAG_ID
 - DAG_RUN_ID

The DAG Run should abort all its tasks running and mark them as "failed".

**Are you willing to submit a PR?**

**Related Issues**


airflow/api_connexion/endpoints/dag_run_endpoint.py
if data.get("dag_ids"):
        dag_ids = set(data["dag_ids"]) & set(readable_dag_ids)
        query = query.filter(DagRun.dag_id.in_(dag_ids))
    else:
        query = query.filter(DagRun.dag_id.in_(readable_dag_ids))
    dag_runs, total_entries = _fetch_dag_runs(
        query,
        data["end_date_gte"],
        data["end_date_lte"],
        data["execution_date_gte"],
        data["execution_date_lte"],
        data["start_date_gte"],
        data["start_date_lte"],
        data["page_limit"],
        data["page_offset"],
        order_by=data.get('order_by', "id"),
    )
    return dagrun_collection_schema.dump(DAGRunCollection(dag_runs=dag_runs, total_entries=total_entries))
@security.requires_access(
    [
        (permissions.ACTION_CAN_EDIT, permissions.RESOURCE_DAG),
        (permissions.ACTION_CAN_CREATE, permissions.RESOURCE_DAG_RUN),
    ]
)
@provide_session
def post_dag_run(dag_id, session):
    """Trigger a DAG."""
    if not session.query(DagModel).filter(DagModel.dag_id == dag_id).first():
        raise NotFound(title="DAG not found", detail=f"DAG with dag_id: '{dag_id}' not found")
    try: