(captiveportal, new) add servername to model

src/opnsense/mvc/app/models/OPNsense/CaptivePortal/CaptivePortal.xml

@@ -48,6 +48,11 @@
                     <Required>N</Required>
                     <ValidationMessage>Please select a valid certificate from the list</ValidationMessage>
                 </certificate>
+                <servername type="TextField">
+                    <Required>N</Required>
+                    <mask>/^([0-9a-zA-Z.,_\-]){0,1024}$/u</mask>
+                    <ValidationMessage>Please enter a valid servername, ip address or leave this option blank</ValidationMessage>
+                </servername>
                 <description type="TextField">
                     <Required>Y</Required>
                     <mask>/^([\t\n\v\f\r 0-9a-zA-Z.,_\x{00A0}-\x{FFFF}]){1,255}$/u</mask>