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.

"Example date format: 2015-11-16T14:34:15+00:00"
            )
            return {"error": error_message}, 400
        task_log_reader = TaskLogReader()
        if not task_log_reader.supports_read:
            return {
                "message": "Task log handler does not support read logs.",
                "error": True,
                "metadata": {"end_of_log": True},
            }
        ti = (
            session.query(models.TaskInstance)
            .filter(
                TaskInstance.task_id == task_id,
                TaskInstance.dag_id == dag_id,
                TaskInstance.execution_date == execution_date,
                TaskInstance.map_index == map_index,
            )
            .join(TaskInstance.dag_run)
            .options(joinedload("trigger"))
            .options(joinedload("trigger.triggerer_job"))
            .first()
        )
        if ti is None:
            return {
                "message": "*** Task instance did not exist in the DB\n",
                "error": True,
                "metadata": {"end_of_log": True},
            }
        try: