Introduce JSON support for the `nodejs/i18n` package

[ovflowd]

Hey @nodejs/i18n 👋

We're working on the efforts of adopting the nodejs/i18n package on @nodejs/nodejs-dev but right now, the package only provides Markdown files which use the complex mixed Markdown + YAML format. And we wanted to avoid creating a custom Markdown parser to support this uncommon syntax.

Currently, the https://nodejs.org/api website provides all the doc pages also in .json format. I wonder how complex it would be to support JSON variants of the doc sources on the nodejs/i18n package API.

I would love to contribute to this if needed.

cc @JohnTitor @zeke