[OpenStackSDK] 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: I0c425ea0be6029758715a5794d8f466847e4eed0

deliverables/stein/openstacksdk.yaml

@@ -53,6 +53,10 @@ releases:
     projects:
       - repo: openstack/openstacksdk
         hash: 25ae60cd4e5acb1231322fb986784747f03d72e5
+  - version: stein-em
+    projects:
+      - repo: openstack/openstacksdk
+        hash: 25ae60cd4e5acb1231322fb986784747f03d72e5
 repository-settings:
   openstack/openstacksdk: {}
 branches: