Add Tempest gate job for stable/wallaby

Now we have stable/wallaby branch ready for devstack
and so does for all service projects.

This commit adds the Tempest testing for stable/wallaby
by adding new jobs running on stable/wallaby version of
openstack.

Depends-On: https://review.opendev.org/c/openstack/devstack/+/784974
Change-Id: Ibb69384be54e284d59950371238a64c041348000

zuul.d/project.yaml

@@ -31,6 +31,8 @@
         - glance-multistore-cinder-import:
             voting: false
             irrelevant-files: *tempest-irrelevant-files
+        - tempest-full-wallaby-py3:
+            irrelevant-files: *tempest-irrelevant-files
         - tempest-full-victoria-py3:
             irrelevant-files: *tempest-irrelevant-files
         - tempest-full-ussuri-py3:
@@ -123,6 +125,7 @@
             irrelevant-files: *tempest-irrelevant-files
     periodic-stable:
       jobs:
+        - tempest-full-wallaby-py3
         - tempest-full-victoria-py3
         - tempest-full-ussuri-py3
         - tempest-full-train-py3

zuul.d/stable-jobs.yaml

@@ -1,4 +1,9 @@
 # NOTE(gmann): This file includes all stable release jobs definition.
+- job:
+    name: tempest-full-wallaby-py3
+    parent: tempest-full-py3
+    override-checkout: stable/wallaby
+
 - job:
     name: tempest-full-victoria-py3
     parent: tempest-full-py3