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.

import itertools
import json
import logging
import math
import re
import sys
import traceback
import warnings
from bisect import insort_left
from collections import defaultdict
from functools import wraps
from json import JSONDecodeError
from typing import Any, Callable, Collection, Iterator, Mapping, MutableMapping, Sequence
from urllib.parse import unquote, urljoin, urlsplit
import configupdater
import flask.json
import lazy_object_proxy
import markupsafe
import nvd3
import sqlalchemy as sqla
from croniter import croniter
from flask import (
    Response,
    abort,
    before_render_template,
    flash,
    g,
    has_request_context,
    make_response,
    redirect,