Fix vite deprecations (#2885)

I wasn't able to fully migrate to esmodules because eslint fails then.
Thus there's still a deprecation warning when running vite.
(https://vitejs.dev/guide/troubleshooting.html#vite-cjs-node-api-deprecated)

web/vite.config.ts

@@ -29,8 +29,8 @@ function externalCSSPlugin() {
   return {
     name: 'external-css',
     transformIndexHtml: {
-      enforce: 'post',
+      order: 'post',
-      transform() {
+      handler() {
         return [
           {
             tag: 'link',