[storlets] Transition Xena to EM

This transition the stable/xena 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 after the transition.

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 20th, 2023.

Change-Id: Ia4d7120cc08fce9fba65333360897b524bf59b92

deliverables/xena/storlets.yaml

@@ -15,6 +15,10 @@ releases:
       - repo: openstack/storlets
         hash: a513114c33d414037ec80bc6c5722dae52a90410
     diff-start: 7.0.0
+  - version: xena-em
+    projects:
+      - repo: openstack/storlets
+        hash: a513114c33d414037ec80bc6c5722dae52a90410
 branches:
   - name: stable/xena
     location: 8.0.0.0rc1