feat: add jsdoc type for config blocks

[andrewbrey]

🔗 Linked issue

Fixes #2

❓ Type of change

• 🐞 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

Add JSDoc type information for the configBlocksToMerge parameter of both configPkg and configApp. Doing this greatly improves the autocomplete experience for users who wish to override any part of the base config.

📝 Checklist

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

[thetutlage]

Thanks for the PR 👍