Add release note for etcd image

Author: markgoddard

releasenotes/notes/etcd-e4927551bf5d020c.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    Adds an ``etcd`` Kolla container image. This can be used for OpenStack
+    service coordination as a tooz backend, or for batched processing of switch
+    configuration in Networking Generic Switch (this requires a downstream NGS
+    patch).