responders: deprecate default_domain_suffix option

:relnote: The option default_domain_suffix is deprecated. Consider using
the more flexible domain_resolution_order instead.

Reviewed-by: Alexey Tikhonov <atikhono@redhat.com>
Reviewed-by: Iker Pedrosa <ipedrosa@redhat.com>

src/man/sssd.conf.5.xml

@@ -418,6 +418,10 @@
                     <varlistentry>
                         <term>default_domain_suffix (string)</term>
                         <listitem>
+                            <para>
+                                Please note that this option is deprecated and
+                                domain_resolution_order should be used.
+                            </para>
                             <para>
                                 This string will be used as a default domain
                                 name for all names without a domain name