SSSCTL: Add the new cached GPOs management commands to release notes

:relnote: The 'sssctl' command line tool has been extended to manage
the cached GPOs. It is now possible to list ('gpo-list') and show
('gpo-show') the cached GPOs, and the 'gpo-remove' and 'gpo-purge'
subcommands are particularly useful as they remove not only the entry
from the database but also the downloaded GPO files.

Signed-off-by: Samuel Cabrero <[email protected]>

Reviewed-by: Sumit Bose <[email protected]>
Reviewed-by: Tomáš Halman <[email protected]>