Define v3 projects_client as library

Migrate identity v3 API projects_client to tempest.lib and implement
unit test for the service clients.
Partially implements blueprint consistent-service-method-names

Change-Id: I9ac7ff64d7adc6de70335f6ccd0c34cae850ec0b
diff --git a/releasenotes/notes/add-new-identity-clients-as-library-3e6559d4bff3e776.yaml b/releasenotes/notes/add-new-identity-clients-as-library-3e6559d4bff3e776.yaml
index 9feb3c3..e000946 100644
--- a/releasenotes/notes/add-new-identity-clients-as-library-3e6559d4bff3e776.yaml
+++ b/releasenotes/notes/add-new-identity-clients-as-library-3e6559d4bff3e776.yaml
@@ -7,3 +7,4 @@
 
       * regions_client(v3)
       * services_client(v3)
+      * projects_client(v3)