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.

chart = nvd3.lineChart(
            name="lineChart",
            x_custom_format=True,
            x_axis_date=True,
            x_axis_format=LINECHART_X_AXIS_TICKFORMAT,
            height=chart_height,
            chart_attr=self.line_chart_attr,
        )
        y_points: dict[str, list[float]] = collections.defaultdict(list)
        x_points: dict[str, list[tuple[int]]] = collections.defaultdict(list)
        for task in dag.tasks:
            task_id = task.task_id
            for ti in tis:
                if ti.task_id != task.task_id:
                    continue
                ts = dag.get_run_data_interval(ti.dag_run).end
                if ti.end_date:
                    dttm = wwwutils.epoch(ti.execution_date)
                    secs = (ti.end_date - ts).total_seconds()
                    x_points[task_id].append(dttm)
                    y_points[task_id].append(secs)
        
        
        y_unit = infer_time_unit([d for t in y_points.values() for d in t])
        
        chart.create_y_axis("yAxis", format=".02f", custom_format=False, label=f"Landing Time ({y_unit})")
        chart.axislist["yAxis"]["axisLabelDistance"] = "-15"
        for task_id in x_points:
            chart.add_serie(
                name=task_id,