fix: set css preload to false (#4524)

After dependabot upgraded us to the new version of Vite, we started
having failures on the preloading of CSS modules on certain lazy loaded
modules. After investigation, it seems like Vite was adding another
stylesheet into the head element when the lazy loaded modules were
requested. These stylesheets had the wrong relative path when the assets
were loaded from our CDN. We are not sure why this fails, but for now we
are turning off cssPreloading.

The impact is small, because we have few lazy loaded modules that
preload the CSS.

frontend/vite.config.ts

@@ -32,6 +32,7 @@ export default mergeConfig(
             outDir: 'build',
             assetsDir: 'static',
             modulePreload: false,
+            cssCodeSplit: false,
         },
         server: {
             open: true,