[train][goal] Define new 'murano-tempest-api-ipv6-only' job in gate

As part of Train community goal 'Support IPv6-Only Deployments and Testing'[1],
Tempest has defined the base job 'devstack-tempest-ipv6' (adding
in Depends-On patch) which will deploy services on IPv6.

This commit adds the new job 'murano-tempest-api-ipv6-only'
run on gate which is derived from 'devstack-tempest-ipv6'.

Verification structure will be:
- 'devstack-IPv6' deploy the service on IPv6
- 'devstack-tempest-ipv6' run will verify the IPv6-only setting and listen address
- 'murano-tempest-api-ipv6-only' will run the tests.

Story: #2005477
Task: #35907

Depends-On: https://review.opendev.org/#/c/671231/

[1] https://governance.openstack.org/tc/goals/train/ipv6-support-and-testing.html

Change-Id: I1efc0f37a23f991fd0a47b6fd8f91c7a75d873ec

.zuul.yaml

@@ -15,10 +15,12 @@
         - murano-tempest-api
         - murano-tempest-cfapi
         - murano-grenade
+        - murano-tempest-api-ipv6-only
     gate:
       queue: murano
       jobs:
         - murano-tempest-api
+        - murano-tempest-api-ipv6-only
 
 - job:
     name: murano-congress-devstack
@@ -68,7 +70,7 @@
     parent: devstack-tempest
     irrelevant-files: *murano-irrelevant-files
     timeout: 7800
-    required-projects:
+    required-projects: &base_required_projects
       - openstack/heat
       - openstack/murano
       - openstack/murano-dashboard
@@ -76,7 +78,7 @@
       - openstack/python-muranoclient
       - openstack/tempest
       - openstack/murano-tempest-plugin
-    vars:
+    vars: &base_vars
       devstack_plugins:
         murano: https://opendev.org/openstack/murano
         heat: https://opendev.org/openstack/heat
@@ -96,6 +98,16 @@
     name: murano-tempest-api
     parent: murano-tempest-base
 
+- job:
+    name: murano-tempest-api-ipv6-only
+    parent: devstack-tempest-ipv6
+    description: |
+      Murano devstack tempest tests job for IPv6-only deployment
+    timeout: 7800
+    irrelevant-files: *murano-irrelevant-files
+    required-projects: *base_required_projects
+    vars: *base_vars
+
 - job:
     name: murano-tempest-cfapi
     parent: murano-tempest-base