Define v3 Groups Client as library

Migrate the v3 API Groups Client to tempest.lib and add unit tests
for the client.

Partially implements blueprint consistent-service-method-names

Change-Id: If964fcb707090f6abb2516b84c26a06f55cdbed6
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 b8a8491..4b26c30 100644
--- a/releasenotes/notes/add-new-identity-clients-as-library-5f7ndha733nwdsn9.yaml
+++ b/releasenotes/notes/add-new-identity-clients-as-library-5f7ndha733nwdsn9.yaml
@@ -6,3 +6,4 @@
     any maintenance changes.
 
       * identity_client(v2)
+      * groups_client(v3)