Use ACM 2.12 on 4.19

We mimick the same approach we use on 4.18.
Eventually we will want to switch to 1.13 but for now this is the least
intrusive choice.

Author: mbaldessari

values-4.19-hub.yaml

@@ -0,0 +1,6 @@
+clusterGroup:
+  subscriptions:
+    acm:
+      name: advanced-cluster-management
+      namespace: open-cluster-management
+      channel: release-2.12