Move v3 roles_client to library interface

v3 roles_client is stable now and good to be moved
as stable library interface.

Partially implements blueprint consistent-service-method-names

Change-Id: I18a4219496754809ae67d99904872bfaf5c61ea9
diff --git a/releasenotes/notes/add-new-identity-clients-as-library-5f7ndha733nwdsn9.yaml b/releasenotes/notes/add-new-identity-clients-as-library-5f7ndha733nwdsn9.yaml
index d1635e3..2e387a4 100644
--- a/releasenotes/notes/add-new-identity-clients-as-library-5f7ndha733nwdsn9.yaml
+++ b/releasenotes/notes/add-new-identity-clients-as-library-5f7ndha733nwdsn9.yaml
@@ -9,3 +9,4 @@
       * groups_client(v3)
       * users_client(v3)
       * identity_client(v3)
+      * roles_client(v3)