fix #7649: ui: active directory realm: expose user attribute name option

AD realms support the 'user_attr' option, which sets the attribute used
as username when syncing users, but it can only be set via the CLI. It
is needed for logging in with the user principal name, if that does not
end with the AD domain: with 'userPrincipalName' as attribute, the users
are synced with their full user principal name, which is then used as
is to bind to the server on login.

Add a field for it, like the LDAP realm has, with the 'sAMAccountName'
default as empty text.

Signed-off-by: Michal Fox <me@dualfroz.com>

www/manager6/dc/AuthEditAD.js

@@ -17,6 +17,13 @@ Ext.define('PVE.panel.ADInputPanel', {
                 emptyText: 'company.net',
                 allowBlank: false,
             },
+            {
+                xtype: 'proxmoxtextfield',
+                name: 'user_attr',
+                fieldLabel: gettext('User Attribute Name'),
+                emptyText: Proxmox.Utils.defaultText + ' (sAMAccountName)',
+                deleteEmpty: !me.isCreate,
+            },
             {
                 xtype: 'proxmoxcheckbox',
                 fieldLabel: gettext('Case-Sensitive'),