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.

"""Get a summary of datasets, including the datetime they were last updated and how many updates
        they've ever had.
        """
        allowed_attrs = ["uri", "last_dataset_update"]
        
        limit = int(request.args.get("limit", 25))
        offset = int(request.args.get("offset", 0))
        order_by = request.args.get("order_by", "uri")
        uri_pattern = request.args.get("uri_pattern", "")
        lstripped_orderby = order_by.lstrip("-")
        updated_after = _safe_parse_datetime(request.args.get("updated_after"), allow_empty=True)
        updated_before = _safe_parse_datetime(request.args.get("updated_before"), allow_empty=True)
        
        limit = 50 if limit > 50 else limit
        uri_pattern = uri_pattern[:4000]
        if lstripped_orderby not in allowed_attrs:
            return {
                "detail": (
                    f"Ordering with '{lstripped_orderby}' is disallowed or the attribute does not "
                    "exist on the model"