Add frozen statuspage JSON response for testing

this means we will be deploying testing config to production, but it
wasn't worth hard-coding a switch for this file in the dokcer build setup.

This file can conveniently be edited to check all the relevant states
of the statuspage widget.

sipa/static/js/agdsn.js

@@ -125,6 +125,8 @@ function handleStatusResponse(components) {
 document.addEventListener('DOMContentLoaded', () => {
     new Statuspage(
         'https://status.agdsn.net/pubapi/services/all',
+        // replace URL by this for testing
+        // "/static/statuspage.json",
         handleStatusResponse
     );
 });