fix(vercel, azure): serve prerendered routes statically

[danielroe]

🔗 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

Current hybrid vercel deployments will always server-render prerendered HTML (though you can get the static html by adding /index.html to the URL). Vercel provides the overrides property to allow us to map clean URLs (without .html or index.html suffix) to static files: https://vercel.com/docs/build-output-api/v3#build-output-configuration/supported-properties/overrides. This PR implements that.

Might also be worth a consistent implementation of accessing which HTML files have been prerendered. (See this line for how we were doing it in Azure - I could easily create a shared context that both presets could use - happy to pick this up.)

📝 Checklist

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

[codecov]

Codecov Report

Merging #500 (a460eea) into main (2dd05fb) will decrease coverage by 0.14%.
The diff coverage is 54.83%.

@@            Coverage Diff             @@
##             main     #500      +/-   ##
==========================================
- Coverage   63.62%   63.48%   -0.15%     
==========================================
  Files          55       55              
  Lines        3634     3620      -14     
  Branches      394      392       -2     
==========================================
- Hits         2312     2298      -14     
+ Misses       1309     1308       -1     
- Partials       13       14       +1     

Impacted Files	Coverage Δ
src/types/nitro.ts	100.00% <ø> (ø)
src/presets/azure.ts	13.67% <13.04%> (-0.04%)	⬇️
src/presets/vercel.ts	65.04% <78.37%> (-8.17%)	⬇️
src/prerender.ts	86.74% <100.00%> (+0.16%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.