The DAGs main page has All/Active/Paused.

It would be nice if we can have also Running Now which will show all the DAGs that have at least 1 in Running of DAG runs:
![Screen Shot 2021-08-25 at 11 30 55](https://user-images.githubusercontent.com/62940116/130756490-647dc664-7528-4eb7-b4d8-515577f7e6bb.png)


For the above example the new DAGs tab of Running Now should show only 2 rows.
The use case is to see easily what DAGs are currently in progress.

TaskInstance.dag_id == dag.dag_id,
                TaskInstance.run_id == dag_run_id,
            )
            completed_tis_ids = [task_id for task_id, in existing_tis]
            tasks_with_no_state = list(set(all_task_ids) - set(completed_tis_ids))
            details = [str(t) for t in tasks_with_no_state]
            return htmlsafe_json_dumps(details, separators=(",", ":"))
    @expose("/dagrun_failed", methods=["POST"])
    @auth.has_access(
        [
            (permissions.ACTION_CAN_EDIT, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_EDIT, permissions.RESOURCE_DAG_RUN),
        ]
    )
    @action_logging
    def dagrun_failed(self):
        """Mark DagRun failed."""
        dag_id = request.form.get("dag_id")
        dag_run_id = request.form.get("dag_run_id")
        confirmed = request.form.get("confirmed") == "true"
        return self._mark_dagrun_state_as_failed(dag_id, dag_run_id, confirmed)
    @expose("/dagrun_success", methods=["POST"])
    @auth.has_access(
        [
            (permissions.ACTION_CAN_EDIT, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_EDIT, permissions.RESOURCE_DAG_RUN),
        ]
    )
    @action_logging
    def dagrun_success(self):