[horizon] Transition Train to End of Life

With the new resolution '2023-07-24 Unmaintained status replaces
Extended Maintenance' [1] the last 3 EM branches (Xena, Wallaby,
Victoria) will transition to Unmaintained, but older branches (Ussuri,
Train) should move to End of Life unless someone steps up as maintainer
of this branch for this project.

To signal this, please add a -1 for this patch if you or the team want
to keep this branch open for further maintenance.
If there is no response from anyone within a reasonable time frame,
then PTLs/release liaisons will be asked to confirm the EOL transition
with their +1.

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

Change-Id: I486f9f6656d619fb396658ec0caf80804539ec49

deliverables/train/horizon.yaml

@@ -45,6 +45,10 @@ releases:
     projects:
       - repo: openstack/horizon
         hash: b72b7e7ac92bd8ce246e9539d2442d729dec4cde
+  - version: train-eol
+    projects:
+      - repo: openstack/horizon
+        hash: f9e08ed8df234052c2a7d204b6922abd3e42775b
 repository-settings:
   openstack/horizon: {}
 cycle-highlights: