docs: Document additional 'server migration' commands

Only 'server migration list' was being documented.

Change-Id: I038ff2bcf7bb852d619004bb00306d2d388135a7
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

Author: stephenfin

doc/source/cli/command-objects/server-migration.rst

@@ -9,4 +9,4 @@ supported: live migration, cold migration, resize and evacuation.
 Compute v2
 
 .. autoprogram-cliff:: openstack.compute.v2
-   :command: server migration list
+   :command: server migration *