Add release note

Author: MoteHue

releasenotes/notes/automation-around-overcloud-host-images-1cb4ed5da1faee94.yaml

@@ -0,0 +1,9 @@
+---
+features:
+  - |
+    Overcloud host images will now automatically be built when changes to
+    ``pulp-repo-versions.yml`` are pushed to ``stackhpc/2025.1``. Once these
+    are built successfully, a PR will be automatically proposed back to SKC.
+    These images will then  be automatically promoted when new host image tags
+    are merged. If the overcloud host image build fails, an alert will be sent
+    to #release-train-alerts on Slack.