Disable karborclient until a fixed version is released

Even though a fix for bug 1705258 has been merged in
python-karborclient, it will take some time to release it and
update the upper-constraints.txt, so I think it is better to
exclude karborclient from the plugin commands doc temporarily.

Change-Id: I092b37b30df785159495c2d681162e144cfe4083
Related-Bug: #1705258

Author: amotoki

doc/source/cli/plugin-commands.rst

@@ -58,11 +58,11 @@ ironic-inspector
 .. list-plugins:: openstack.baremetal_introspection.v1
    :detailed:
 
-karbor
-------
-
-.. list-plugins:: openstack.data_protection.v1
-   :detailed:
+.. karbor
+.. ------
+.. bug 1705258: Exclude karborclient 0.4.0 until a fixed version is released.
+.. .. list-plugins:: openstack.data_protection.v1
+..    :detailed:
 
 mistral
 -------