**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**


tests/api_connexion/endpoints/test_dag_run_endpoint.py
dag_runs.append(
                    DagRun(
                        dag_id='TEST_DAG_ID_' + str(i),
                        run_id='TEST_DAG_RUN_ID_' + str(i),
                        run_type=DagRunType.MANUAL,
                        execution_date=timezone.parse(self.default_time_2),
                        start_date=timezone.parse(self.default_time),
                        external_trigger=True,
                        state=state,
                    )
                )
        if commit:
            with create_session() as session:
                session.add_all(dag_runs)
                session.add_all(dags)
        return dag_runs
class TestDeleteDagRun(TestDagRunEndpoint):
    def test_should_respond_204(self, session):
        session.add_all(self._create_test_dag_run())
        session.commit()
        response = self.client.delete(
            "api/v1/dags/TEST_DAG_ID/dagRuns/TEST_DAG_RUN_ID_1", environ_overrides={'REMOTE_USER': "test"}
        )
        assert response.status_code == 204
        
        response = self.client.get(
            "api/v1/dags/TEST_DAG_ID/dagRuns/TEST_DAG_RUN_ID_1", environ_overrides={'REMOTE_USER': "test"}
        )
        assert response.status_code == 404
    def test_should_respond_404(self):