Investigate/test CSP use with the starter

[mitchmac]

Content security policies provide an extra layer of security for various theoretical vulnerabilities. We could provide a sample CSP implementation in the starter or use the starter to guide documentation on potential CSP approaches.

[DirtyF]

Next.js has security headers: https://nextjs.org/docs/advanced-features/security-headers

[jeffsee55]

provide an extra layer of security for various theoretical vulnerabilities

We may run into a few snags with unsafe-inline. Looks like that's still an issue

styled-components/styled-components#887 (comment)