Add microversion rule when adding attr to request

This patch adds microversion bump rule when adding a new attribute
to a request body.

Change-Id: I8e4de474569bd1d7b10bc4a2610cc7fba10912ee

doc/source/api_microversion_dev.rst

@@ -56,6 +56,10 @@ changed. The user contract covers many kinds of information such as:
 
   - new headers accepted on a request
 
+  - the list of attributes and data structures accepted.
+
+    Example: adding a new attribute 'locked': True/False to the request body
+
 - the Response
 
   - the list of attributes and data structures returned