(create-zephyr-app) Prompt choice between yaml and json

[marvin-j97]

I personally quite dislike yaml, so the first thing I'd always do after using create-zephyr-app would be converting those back to json. It would be nice to be able to choose between json and yaml, and write prettierrc.yml and eslintrc.yml on demand using JSON or YAML (https://www.npmjs.com/package/yaml). It would also help in the future for modifying those configs (like choosing different rule sets if the user wants to).

[kakengloh]

Yeah we should prompt user for some config preference, planning to refactor create-zephyr-app soon. I think create-astro is really great, might be a good reference.