docs: add Sevalla deployment documentation

[olawanlejoel]

🔗 Linked issue

❓ 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)
• [x] ✨ New feature (a non-breaking change that adds functionality)
• [ ] 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Sevalla is a modern cloud platform for hosting applications, databases, object storage, and static sites, offering a simple and scalable deployment experience.

This PR adds documentation for deploying Nuxt applications to Sevalla. It introduces a new markdown file under the deployment guides and includes the relevant integration image. This helps users understand how to deploy their Nuxt projects on Sevalla, expanding the available deployment options in the documentation.

[atinux]

Pending https://github.com/nitrojs/nitro/pull/3554