Use Volume V3 API in OpenStack exporter

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
(cherry picked from commit 4410ca7)

Author: neoaggelos

ansible/roles/prometheus/templates/clouds.yml.j2

@@ -3,6 +3,7 @@ clouds:
    region_name: {{ openstack_region_name }}
    identity_api_version: 3
    identity_interface: internal
+   volume_api_version: 3
    auth:
      username: {{ keystone_admin_user }}
      password: {{ keystone_admin_password }}

releasenotes/notes/bug-1938194-80dba28f9cdd434c.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    Use Volume V3 API in OpenStack exporter. Volume V2 API has been removed
+    since OpenStack Wallaby.
+    `LP#1938194 <https://bugs.launchpad.net/kolla-ansible/+bug/1938194>`__