SECRETS: Add allowed_sec_users_options
    
    There are options (the proxying related ones) that only apply to the
    secrets' subsections. In order to make config API able to catch those,
    let's create a new section called allowed_sec_users_options) and move
    there these proxying options.
    
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>