feat(api): support comments in bulk environment variable endpoints

Add support for optional comment field on environment variables created or
updated through the bulk API endpoints. Comments are validated to a maximum
of 256 characters and are nullable. Updates preserve existing comments when
not provided in the request.

app/Http/Controllers/Api/ServicesController.php

@@ -1362,6 +1362,7 @@ class ServicesController extends Controller
                 'is_literal' => 'boolean',
                 'is_multiline' => 'boolean',
                 'is_shown_once' => 'boolean',
+                'comment' => 'string|nullable|max:256',
             ]);
 
             if ($validator->fails()) {