examples: Add example polkit ACL rules

examples: Add example polkit ACL rules

Creating ACL rules is not exactly easy and existing examples are pretty
simple. This patch adds a somewhat complex example which defines several
roles. Admins can do everything, operators can do basic operations
on any domain and several groups of users who act as operators but only
on a limited set of domains.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>