Move oldest stable testing to stable/2023.1

stable/zed is transioning to unmaintained state and
stable/2023.1 is going to be the oldest supported stable
release. Updating the stable job here accordingly.

Also, defining the stable branch testing job here itself
to avoid job definition dependency in Tempest repo.

Change-Id: Ie179b4acd8d17a8b627ea70c9b74a432d2b29f6c

.zuul.yaml

@@ -20,6 +20,15 @@
     required-projects:
       - openstack/stackviz
 
+- job:
+    name: tempest-full-oldest-stable
+    parent: tempest-full-py3
+    # NOTE(gmann): This job supposed to test the oldest supported stable
+    # release. We need to update the override-checkout once oldest
+    # stable is moved to next stable release.
+    override-checkout: stable/2023.1
+    nodeset: openstack-single-node-jammy
+
 - project:
     templates:
       - publish-openstack-docs-pti
@@ -44,7 +53,7 @@
             - ^.coveragerc$
             - ^.gitignore$
             - ^.gitreview$
-      - tempest-full-zed:
+      - tempest-full-oldest-stable:
           irrelevant-files: *irrelevant-files
     gate:
       jobs: