chore(docs): add examples for built-in pages

[halvaradop]

☕️ Reasoning

This pull request adds code examples to the Built-in Pages section for the frameworks supported by Auth.js, including Next.js, Qwik, and SvelteKit. The examples demonstrate how automatic page generation works when the user provides providers in their configuration file.

Additionally, to avoid code repetition across frameworks, the provider configurations are now written in a separate file.

On the other hand, the code for the SignInButton component in the Next.js example has been removed. The focus is on demonstrating how to set up built-in pages. If you believe the SignInButton component is relevant, please let me know, and I will make the necessary changes.

🧢 Checklist

• [x] Documentation
• [ ] Tests
• [x] Ready to be merged

🎫 Affected issues

📌 Resources

• Security guidelines
• Contributing guidelines
• Code of conduct
• Contributing to Open Source

[vercel[bot]]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
auth-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Sep 11, 2024 4:03pm

1 Skipped Deployment

Name	Status	Preview	Comments	Updated (UTC)
next-auth-docs	⬜️ Ignored (Inspect)	Visit Preview		Sep 11, 2024 4:03pm

[vercel[bot]]

@halvaradop is attempting to deploy a commit to the authjs Team on Vercel.

A member of the Team first needs to authorize it.

[halvaradop]

I have made the changes based on your suggestions. 🧙‍♂️