[horizon] Transition Victoria to EM

This transition the victoria branch to extended maintenance.
Changes for bugfixes and things the team deems important are
still encouraged, but there will no longer be official releases
off of the branch.

Please +1 if the team is ready for us to proceed with this
transition, or -1 if there are any final backports currently in
flight that we should wait for. For the latter case, please
update the patch with the new commit hash after doing a final
release to get those changes out so we know to proceed with the
transition.

The transition deadline is April 27th, 2022.

Change-Id: I71ae8712c28b875c6c594dbdd5f8fc8cad7d51d5

deliverables/victoria/horizon.yaml

@@ -38,6 +38,10 @@ releases:
     projects:
       - repo: openstack/horizon
         hash: c9ebeb1fa3de5ead102fef2027c8e5320c3038e1
+  - version: victoria-em
+    projects:
+      - repo: openstack/horizon
+        hash: c9ebeb1fa3de5ead102fef2027c8e5320c3038e1
 branches:
   - name: stable/victoria
     location: 18.6.0