feat: experimental bundled storage

[pi0]

🔗 Linked issue

❓ Type of change

• 📖 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

This PR introduces a new (experimental) bundledStorage option. It will take a snapshot of storage before starting the build (after prerendering) and makes it available at runtime by copying to output bundle. Mostly useful to snapshot cache for faster initial response.

Leftovers:

• Overlay Storage (Overlay storage unstorage#8)
• Add docs

Future enhancements:

• Use a virtual object to avoid creating a temporary .nitro/snapshot directory and directly bundle server assets from memory

Other fixes:

• Set the correct preset value to nitro.options.preset
• Avoid copying server assets for prerendering step
• Added a new devStorage option, for build-time (dev, prerender and build) available storage
• Partially refactor storage logic to src/storage.ts from rollup plugin

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.