Use getStaticProps in static pages

## Background Information
Some pages are always static and because we run a [Custom Nextjs Server](https://nextjs.org/docs/pages/building-your-application/configuring/custom-server) we do not get automated static generation. In order to achieve that we need to [explicitly define that for the static pages](https://nextjs.org/docs/pages/building-your-application/data-fetching/get-static-props).

## What
List of pages that are static:
- 400s and 500s errors
- Code of Conduct
- About
- Privacy Policy