Spec file: add support for sss_ssh_knownhosts
    
    sss_ssh_knownhostsproxy will be deprecated in favor of sss_ssh_knownhosts. This commit
    implements a mechanism to apply the change when upgrading from older versions.
    
    Fixes: https://pagure.io/freeipa/issue/9536
    Signed-off-by: Francisco Trivino <ftrivino@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>