Define v2 images_client as library

Image v2 API's images_client has good interfaces now, then this patch
makes the client as a library.

Partially implements blueprint consistent-service-method-names

Change-Id: I44852225ac8d3cb45bd04685e214fb39576b8206
diff --git a/releasenotes/notes/image-clients-as-library-86d17caa26ce3961.yaml b/releasenotes/notes/image-clients-as-library-86d17caa26ce3961.yaml
index b50ed38..1ba790c 100644
--- a/releasenotes/notes/image-clients-as-library-86d17caa26ce3961.yaml
+++ b/releasenotes/notes/image-clients-as-library-86d17caa26ce3961.yaml
@@ -7,6 +7,7 @@
     without any maintenance changes.
 
       * image_members_client
+      * images_client
       * namespaces_client
       * resource_types_client
       * schemas_client