**Description**

I have noticed that the stable REST API doesn't have the ability to run a task (which is possible from the airflow web interface.
I think it would be nice to have either:
- Run task 
- Run all failing tasks (rerun from point of failure)
this ability for integrations.

**Use case / motivation**

I would like the ability to identify the failing tasks on a specific DAG Run and rerun only them.
I would like to do it remotely (non-interactive) using the REST API.
I could write a script that run only the failing tasks, but I couldn't find a way to "Run" a task, when I have the task instance ID.

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

Not at this stage

**Related Issues**



tests/api_connexion/endpoints/test_task_instance_endpoint.py
{
                'dag_id': 'example_python_operator',
                'dag_run_id': 'TEST_DAG_RUN_ID_1',
                'execution_date': '2020-01-02T00:00:00+00:00',
                'task_id': 'sleep_for_0',
            },
            {
                'dag_id': 'example_python_operator',
                'dag_run_id': 'TEST_DAG_RUN_ID_2',
                'execution_date': '2020-01-03T00:00:00+00:00',
                'task_id': 'sleep_for_1',
            },
            {
                'dag_id': 'example_python_operator',
                'dag_run_id': 'TEST_DAG_RUN_ID_3',
                'execution_date': '2020-01-04T00:00:00+00:00',
                'task_id': 'sleep_for_2',
            },
            {
                'dag_id': 'example_python_operator',
                'dag_run_id': 'TEST_DAG_RUN_ID_4',
                'execution_date': '2020-01-05T00:00:00+00:00',
                'task_id': 'sleep_for_3',
            },
        ]
        for task_instance in expected_response:
            assert task_instance in response.json["task_instances"]
        assert 5 == len(response.json["task_instances"])
        assert 0 == failed_dag_runs, 0
    def test_should_raises_401_unauthenticated(self):