adtrust.py: mention restarting sssd when adding trust agents
    
    After adding a replica to AD trust agent, the warning
    message does not mention that restarting sssd is mantatory
    for the trust agent to work. Fix the string.
    
    Fixes: https://pagure.io/freeipa/issue/8148
    Signed-off-by: François Cami <fcami@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>