Use vitejs instead of react-scripts

- react-scripts are not maintained anymore
- vitejs is well suited for single page applications

Fixes #335

See https://darekkay.com/blog/create-react-app-to-vite/

Change-Id: Ib884748e373094a640b576894ff67b98c3584ec8

docker-compose.yml

@@ -14,8 +14,6 @@ services:
     # if you're building on an architecture other than amd64, make sure
     # to define a maximum ram for node. otherwise the build will fail.
     #   - NODE_OPTIONS="--max_old_space_size=1024"
-    # default is .
-    #   - PUBLIC_URL=/synapse-admin
     ports:
       - "8080:80"
     restart: unless-stopped