[cinder] Add user cinder to role cloud_volume_admin
[cinder] Add user cinder to role cloud_volume_admin

This is necessary for the implemented (c4bcde7f) liveness probes for the
cinder-volume containers, as the `services:index` endpoint has
restrictions in the code (when querying the DB), that the user validates
the policy `context_is_admin`.

sapcc/helm-charts,sapcc/helm-charts,sapcc/helm-charts,sapcc/helm-charts