Update JS quick start guides to use the new split format

### SDK

JavaScript SDK

### Description

Let's update the JavaScript Quick start guides (wizard and manual setup) to use the new split layout.

References:
- [Next.js](https://docs.sentry.io/platforms/javascript/guides/nextjs/)
- [React](https://docs.sentry.io/platforms/javascript/guides/react/)

### Suggested Solution

_No response_