Define v3 regions_client as library

Migrate v3 API regions_client to tempest.lib

Partially implements blueprint consistent-service-method-names

Change-Id: I3eb2d1156d5a5c3e94632e984a9feb31d55e5542
diff --git a/releasenotes/notes/add-new-identity-clients-as-library-3e6559d4bff3e776.yaml b/releasenotes/notes/add-new-identity-clients-as-library-3e6559d4bff3e776.yaml
new file mode 100644
index 0000000..da0e85b
--- /dev/null
+++ b/releasenotes/notes/add-new-identity-clients-as-library-3e6559d4bff3e776.yaml
@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    Define identity service clients as libraries
+    Add new service clients to the library interface so the other projects can use these modules as stable libraries without
+    any maintenance changes.
+
+      * regions_client(v3)