docs: merge deployment pages in getting started

[clemcode]

🔗 Linked issue

#6904

❓ Type of change

• [x] 📖 Documentation (updates to the documentation or readme)
• [ ] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [ ] 👌 Enhancement (improving an existing functionality like performance)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

As planned in #6904, this PR merges the different deployment guides and moves them to Getting started.

The different hosting providers pages mostly linked to the Nitro website and have been removed in favor of a direct link to Nitro docs.

[codesandbox[bot]]

  Open in CodeSandbox Web Editor | VS Code | VS Code Insiders

[netlify[bot]]

✅ Deploy Preview for nuxt3-docs ready!

Name	Link
🔨 Latest commit	14547a83a97a07cd0d1defa74e7d7dfa13f1d46d
🔍 Latest deploy log	https://app.netlify.com/sites/nuxt3-docs/deploys/63319956d9b8710008c6d94e
😎 Deploy Preview	https://deploy-preview-7765--nuxt3-docs.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.