Admin-Server: Prevent caching of index.html also for fallback (#281)

Previously, the default cache-control header was used (public,
max-age=0), which can lead to caching in certain situations (see
https://stackoverflow.com/a/1383359/5562283)

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admin/server/server.js

@@ -53,7 +53,7 @@ app.use(
 
 // As a fallback, route everything to index.html
 app.get("*", (req, res) => {
-    res.sendFile(`index.html`, { root: `${__dirname}/../build/` });
+    res.sendFile(`index.html`, { root: `${__dirname}/../build/`, headers: { "cache-control": "no-store" } });
 });
 
 app.listen(port, () => {