[congress] Transition Train to EM

This transition the train 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: I93cd72aad2929979abd83ecc79638a7d6bf62612

deliverables/train/congress-dashboard.yaml

@@ -16,6 +16,10 @@ releases:
       - repo: openstack/congress-dashboard
         hash: 8f0ba864891c432f07bec2975fc996e18b94e52b
     diff-start: 4.0.0
+  - version: train-em
+    projects:
+      - repo: openstack/congress-dashboard
+        hash: 8f0ba864891c432f07bec2975fc996e18b94e52b
 branches:
   - name: stable/train
     location: 5.0.0.0rc1