[ec2-api] Transition Stein to EM

This transition the stein 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.

Change-Id: Iee18f6ec824a9b912df64d876f50e7307720071d

deliverables/stein/ec2-api.yaml

@@ -11,6 +11,10 @@ releases:
     projects:
       - repo: openstack/ec2-api
         hash: 46af2c326f413fb993e6dbe7d14cdc4b7e3f4ace
+  - version: stein-em
+    projects:
+      - repo: openstack/ec2-api
+        hash: 46af2c326f413fb993e6dbe7d14cdc4b7e3f4ace
 branches:
   - location: 8.0.0
     name: stable/stein