finish qos_rule_type_details extension api-ref
finish qos_rule_type_details extension api-ref

The current api-ref for qos_rule_type_details is incomplete; see bug
description.
This patch completes the qos_rule_type_details api-ref by documenting
the extension and ensuring the 'drivers' param is documented and
included in the sample JSON responses.

Change-Id: I954cf8e11ac5a075f3cd423104f6a2b2c1eb7710
Closes-Bug: #1733387

openstack/neutron-lib,openstack/neutron-lib,openstack/neutron-lib,openstack/neutron-lib