RAZZLE_PUBLIC_URL is overridden by server.jsx code

[ichim-david]

Describe the bug
Volto should use the razzle env for setting publicURL

To Reproduce
Steps to reproduce the behavior:
Start Volto with:
RAZZLE_PUBLIC_URL=http://backend:8080/SITE pnpm start
inspect within the browser devtools:
window.env.publicURL
locally you will see it being http://localhost:3000 instead of http://backend:8080/SITE

Expected behavior

1. Remove
   https://github.com/plone/volto/blob/main/packages/volto/src/server.jsx#L162
   Since we define config.settings.publicURL
   https://github.com/plone/volto/blob/main/packages/volto/src/config/index.js#L57

2. use only config.settings.publicURL here
   https://github.com/plone/volto/blob/main/packages/volto/src/server.jsx#L293

[davisagli]

@ichim-david It makes sense to me that RAZZLE_PUBLIC_URL should take precedence if it was set. But let's not remove using res.locals.detectedHost -- that's important if RAZZLE_PUBLIC_URL was not set.