[stable/2023.1] feat: specify api microversion for nova client in magnum conf (#2083)

This is an automated cherry-pick of #1822
/assign okozachenko1203
diff --git a/roles/magnum/vars/main.yml b/roles/magnum/vars/main.yml
index 2f348ed..95582ac 100644
--- a/roles/magnum/vars/main.yml
+++ b/roles/magnum/vars/main.yml
@@ -69,6 +69,7 @@
         endpoint_type: internalURL
         region_name: "{{ openstack_helm_endpoints_neutron_region_name }}"
       nova_client:
+        api_version: 2.15
         endpoint_type: internalURL
         region_name: "{{ openstack_helm_endpoints_nova_region_name }}"
       octavia_client: