fix(prerender): allow ignoring errors in prerender:generate hook

[danielroe]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 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)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

We currently allow skipping route generation in prerender:generate, but it's not possible to granularly ignore errors on a per-route basis. Instead we either turn off failOnError for the entire build or not.

This change allows the user (or integration) to ignore particular errors based on their own criteria, without disabling failOnError protection entirely.

You might also consider this an enhancement - feel free to amend 🙏

background: was debugging some strange errors prerendering /_ipx routes that only occured in Vercel on my personal site - I am happy ignoring these but would like any other errors to be build-breaking ones.

📝 Checklist

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

[pi0]

(can we rebase it for v2?)