[horizon] Transition Yoga to Unmaintained

With the new TC resolution the community replaces Extended Maintenance
with Unmaintained status [1].

So this patch transitions stable/yoga branch to Unmaintained as follows:
- tip of the stable/yoga branch is tagged with yoga-eom tag
- unmaintained/yoga branch will be cut from yoga-eom tag
- stable/yoga branch will be deleted

Some further notes:
- there will no longer be official releases off of yoga branch
- backports can be pushed against unmaintained/yoga branch
- openstack-unmaintained-core and <project>-unmaintained-core groups
  will have the rights to merge patches

For further details please read the resolution [1] & review and +1 this
patch if this is correct as soon as possible.

[1] https://governance.openstack.org/tc/resolutions/20230724-unmaintained-branches.html

Change-Id: I9e36911fe4c891cc8098de1442c997466b268377

deliverables/yoga/horizon.yaml

@@ -34,7 +34,13 @@ releases:
     projects:
       - repo: openstack/horizon
         hash: eb57aa5300be01a349684a8aa07d9a973357cf7d
+  - version: yoga-eom
+    projects:
+      - repo: openstack/horizon
+        hash: eb57aa5300be01a349684a8aa07d9a973357cf7d
 branches:
   - name: stable/yoga
     location: 22.0.0
+  - name: unmaintained/yoga
+    location: yoga-eom
 release-notes: https://docs.openstack.org/releasenotes/horizon/yoga.html