feat: allow customising generated tsConfig

[danielroe]

🔗 Linked issue

nuxt/nuxt#21074

❓ 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

Users or consuming frameworks might need to customise the generated tsConfig - this makes that possible via nitro options.

📝 Checklist

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

[codecov]

Codecov Report

Merging #1266 (86d61ab) into main (2ad4389) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1266      +/-   ##
==========================================
+ Coverage   76.83%   76.90%   +0.06%     
==========================================
  Files          68       68              
  Lines        6829     6832       +3     
  Branches      692      693       +1     
==========================================
+ Hits         5247     5254       +7     
+ Misses       1580     1577       -3     
+ Partials        2        1       -1     

Impacted Files	Coverage Δ
src/build.ts	85.21% <100.00%> (ø)
src/options.ts	94.33% <100.00%> (+0.01%)	⬆️
src/types/nitro.ts	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

[pi0]

(CI on main is failing so edge will be delivered in a bit)