Add `prefix' option when creating the resource config for web2's database

refs #7163

application/forms/Setup/DbResourcePage.php

@@ -63,6 +63,14 @@ class DbResourcePage extends Form
 
         $resourceForm = new DbResourceForm();
         $this->addElements($resourceForm->createElements($formData)->getElements());
+        $this->addElement(
+            'hidden',
+            'prefix',
+            array(
+                'required'  => true,
+                'value'     => 'icingaweb_'
+            )
+        );
     }
 
     /**