Converted Blog example over to TypeScript to match the Contribution guidelines.
I also simplified the example by removing `_document.js` and prettier from `package.json`.
## Documentation / Examples
- [X] Make sure the linting passes by running `pnpm lint`
- [X] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)
