Add schema for compute 2.45 microversion

Compute microversion 2.45 changed the response
of create image and create backup APIs.

create image schema already covered
- https://github.com/openstack/tempest/blob/fec2c93cdcc14ad08d0a35136ee287525e7a4879/tempest/lib/api_schema/response/compute/v2_45/images.py

This patch adds the schema for create backup API.

Partially Implements: blueprint fix-microversion-gap

Change-Id: Icfeec8957c58472e7f176680d48745b5c5350b55
diff --git a/doc/source/microversion_testing.rst b/doc/source/microversion_testing.rst
index ae9f26f..c9db836 100644
--- a/doc/source/microversion_testing.rst
+++ b/doc/source/microversion_testing.rst
@@ -374,6 +374,10 @@
 
   .. _2.42: https://docs.openstack.org/nova/latest/reference/api-microversion-history.html#maximum-in-ocata
 
+  * `2.45`_
+
+  .. _2.45: https://docs.openstack.org/nova/latest/reference/api-microversion-history.html#id41
+
   * `2.47`_
 
   .. _2.47: https://docs.openstack.org/nova/latest/reference/api-microversion-history.html#id43