Add placeholder to add segment dialog

'Autogenerated' placeholder is shown when adding new segment.

https://fedorahosted.org/freeipa/ticket/5867

Reviewed-By: Petr Vobornik <pvoborni@redhat.com>

ipaserver/plugins/internal.py

@@ -739,6 +739,7 @@ class i18n_messages(Command):
                 "user": _("Who"),
             },
             "topology": {
+                "autogenerated": _("Autogenerated"),
                 "segment_details": _("Segment details"),
                 "replication_config": _("Replication configuration"),
                 "insufficient_domain_level" : _("Managed topology requires minimal domain level ${domainlevel}"),