**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**



airflow/models/dag.py
Note that operators have the same hook, and precede those defined
        here, meaning that if your dict contains `'depends_on_past': True`
        here and `'depends_on_past': False` in the operator's call
        `default_args`, the actual value will be `False`.
    :type default_args: dict
    :param params: a dictionary of DAG level parameters that are made
        accessible in templates, namespaced under `params`. These
        params can be overridden at the task level.
    :type params: dict
    :param concurrency: the number of task instances allowed to run
        concurrently
    :type concurrency: int
    :param max_active_runs: maximum number of active DAG runs, beyond this
        number of DAG runs in a running state, the scheduler won't create
        new active DAG runs
    :type max_active_runs: int
    :param dagrun_timeout: specify how long a DagRun should be up before
        timing out / failing, so that new DagRuns can be created. The timeout
        is only enforced for scheduled DagRuns.
    :type dagrun_timeout: datetime.timedelta
    :param sla_miss_callback: specify a function to call when reporting SLA
        timeouts.
    :type sla_miss_callback: types.FunctionType
    :param default_view: Specify DAG default view (tree, graph, duration,
                                                   gantt, landing_times), default tree
    :type default_view: str
    :param orientation: Specify DAG orientation in graph view (LR, TB, RL, BT), default LR
    :type orientation: str
    :param catchup: Perform scheduler catchup (or only run latest)? Defaults to True
    :type catchup: bool