This PR updates the `cms-contentful` example to use:
- App Router
- TypeScript
- Draft Mode (previously Preview Mode)
- ISR / Data Cache (revalidations through `revalidateTag`)
Further, it combines many separate files into more manageable single files, and tries to better bucket provider-specific logic into the `lib/` folder. I'm hoping this can be the foundation for re-writing the rest of the `cms-*` examples to use App Router.
Overall, the code is much easier to reason about IMO. Pretty happy with the change. I sprinkled some `any`'s throughout here, but if someone wants to make it better, go for it!
https://app-router-contentful.vercel.app/
