Add tests for "new" Transfers API (mv 3.55)

Add a client and test class for Block Storage API v3.55

Change-Id: I4179799bc40a50bdbeecaee461d32e827269cc1f
diff --git a/doc/source/microversion_testing.rst b/doc/source/microversion_testing.rst
index f37342e..0b80b72 100644
--- a/doc/source/microversion_testing.rst
+++ b/doc/source/microversion_testing.rst
@@ -463,3 +463,7 @@
   * `3.20`_
 
   .. _3.20:  https://docs.openstack.org/cinder/latest/contributor/api_microversion_history.html#id19
+
+  * `3.55`_
+
+  .. _3.55:  https://docs.openstack.org/cinder/latest/contributor/api_microversion_history.html#maximum-in-rocky