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.

with create_session() as session:
        for dag_id in TEST_FILTER_DAG_IDS:
            filename = os.path.join(tmpdir, f"{dag_id}.py")
            with open(filename, "w") as f:
                f.writelines("airflow DAG")
            _process_file(filename, session)
@pytest.fixture()
def broken_dags_with_read_perm(tmpdir, working_dags_with_read_perm):
    with create_session() as session:
        for dag_id in TEST_FILTER_DAG_IDS:
            filename = os.path.join(tmpdir, f"{dag_id}.py")
            with open(filename, "w") as f:
                f.writelines("airflow DAG")
            _process_file(filename, session)
def test_home_filter_tags(working_dags, admin_client):
    with admin_client:
        admin_client.get("home?tags=example&tags=data", follow_redirects=True)
        assert "example,data" == flask.session[FILTER_TAGS_COOKIE]
        admin_client.get("home?reset_tags", follow_redirects=True)
        assert flask.session[FILTER_TAGS_COOKIE] is None
def test_home_importerrors(broken_dags, user_client):
    
    resp = user_client.get("home", follow_redirects=True)
    check_content_in_response("Import Errors", resp)
    for dag_id in TEST_FILTER_DAG_IDS:
        check_content_in_response(f"/{dag_id}.py", resp)
@pytest.mark.parametrize("page", ["home", "home?status=active", "home?status=paused", "home?status=all"])
def test_home_importerrors_filtered_singledag_user(broken_dags_with_read_perm, client_single_dag, page):