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.

"action_varexport": "read",
    }
    base_permissions = [
        permissions.ACTION_CAN_CREATE,
        permissions.ACTION_CAN_READ,
        permissions.ACTION_CAN_EDIT,
        permissions.ACTION_CAN_DELETE,
        permissions.ACTION_CAN_ACCESS_MENU,
    ]
    list_columns = ["key", "val", "description", "is_encrypted"]
    add_columns = ["key", "val", "description"]
    edit_columns = ["key", "val", "description"]
    show_columns = ["key", "val", "description"]
    search_columns = ["key", "val"]
    base_order = ("key", "asc")
    def hidden_field_formatter(self):
        """Formats hidden fields."""
        key = self.get("key")
        val = self.get("val")
        if secrets_masker.should_hide_value_for_key(key):
            return Markup("*" * 8)
        if val:
            return val
        else:
            return Markup('<span class="label label-danger">Invalid</span>')
    formatters_columns = {
        "val": hidden_field_formatter,
    }
    validators_columns = {"key": [validators.DataRequired()]}
    def prefill_form(self, form, request_id):