[neutron] 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.

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

Change-Id: I40169aeccc5c80a6623e8fff81c7f5973e7217b2

deliverables/xena/neutron-vpnaas-dashboard.yaml

@@ -19,7 +19,14 @@ releases:
     projects:
       - repo: openstack/neutron-vpnaas-dashboard
         hash: f0a1186b5f0328837fe4038d4dda766b4cb8987f
+  - version: xena-eom
+    projects:
+      - repo: openstack/neutron-vpnaas-dashboard
+        hash: f0a1186b5f0328837fe4038d4dda766b4cb8987f
 branches:
   - name: stable/xena
     location: 5.0.0.0rc1
-release-notes: https://docs.openstack.org/releasenotes/neutron-vpnaas-dashboard/xena.html
+  - name: unmaintained/xena
+    location: xena-eom
+release-notes:
+  https://docs.openstack.org/releasenotes/neutron-vpnaas-dashboard/xena.html