[Puppet OpenStack] Transition EM branches to Unmaintained

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

So this patch transitions victoria, wallaby, and xena EM branches to
Unmaintained as follows:
- tip of the given branch will be tagged with <series>-eom tag
- unmaintained/<series> branch will be cut from <series>-eom tag
- stable/<series> branch will be deleted

Some further notes:
- stable policy still applies
- backports can be pushed against unmaintained/<series> branch
- openstack-unmaintained-core group 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.

NOTE(elod.illes): the deliverables, which were marked as retired, no
need to move to Unmaintained so this patch EOLs them directly.

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

Change-Id: Ie1e6d394a63bcb29b75bb5e5151b1bb993a72696

deliverables/xena/puppet-designate.yaml

@@ -34,7 +34,13 @@ releases:
     projects:
       - repo: openstack/puppet-designate
         hash: 734e498ac69fb0ef8d7cd4e66f66102aae655d08
+  - version: xena-eom
+    projects:
+      - repo: openstack/puppet-designate
+        hash: 734e498ac69fb0ef8d7cd4e66f66102aae655d08
 branches:
   - name: stable/xena
     location: 19.4.0
+  - name: unmaintained/xena
+    location: xena-eom
 release-notes: https://docs.openstack.org/releasenotes/puppet-designate/xena.html