docs: panel-area link target

Add the `target` option and clarify that absolute URLs are possible (e.g. for external links to analytics, etc.)

Author: evolkmann

content/docs/2_reference/7_plugins/1_extensions/0_panel-areas/reference-extension.txt

@@ -48,9 +48,12 @@ Kirby::plugin('yourname/todos', [
         // show / hide from the menu
         'menu' => true,
 
-        // link to the main area view
+        // link to the main area view (can also be an absolute URL)
         'link' => 'todos',
 
+        // optional; to open the link in a new tab
+        'target' => '_blank',
+
         // views
         'views' => [
           [