Add release note for log_req_body kwarg

This commit updates the release note from change
I7cbd3656463a51d18b4d72f45a324145283fc7eb. That commit was missing a
release note for the extra kwarg and concentrated only on the security
fix. This commit addresses that oversight. In addition the security note
is removed from the release notes because it's not addressing a released
security issue, just a short lived one introduced during development of
the pending release.

Change-Id: Id2d34eb911435e5a1036d0494a7df43eda2ebf0a

releasenotes/notes/fix-credential-logging-98089c897d801355.yaml

@@ -1,6 +1,9 @@
 ---
-security:
+features:
   - |
-    Recently we moved the logging of API request in rest_client's
-    raw_request which end up logging the credentials also from
-    Token client request. This issue has been fixed now.
+    A new kwarg, ``log_req_body``, was added to the
+    ``tempest.lib.common.rest_client.RestClient`` method ``raw_request()``.
+    This kwarg takes in a string which will be used in place of the request
+    body, which is logged by default. The intent of this option is to be used
+    for security reasons to avoid logging sensitive information that are part
+    of request bodies.