Documentation/x86: Documentation for MON group move feature

Describe new support for moving MON groups to a new parent CTRL_MON
group and its restrictions.

Signed-off-by: Peter Newman <peternewman@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Link: https://lore.kernel.org/r/20230419125015.693566-4-peternewman@google.com