Kolla has removed the Volume V2 API by default since OpenStack Wallaby.
However, openstack-exporter attempts to use the Volume V2 API by
default, resulting in clean installs failing to fetch Cinder metrics
in Prometheus.
This patch updates the clouds.yml configuration file for
openstack-exporter to use the Volume V3 API instead.
Closes-Bug: #1938194
Change-Id: Ifbb601be3ef1a1e853d5a7e832adf556c0ae38b9