docs: use defineEventHandler instead of eventHandler

[Barbapapazes]

🔗 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

Hello, since functions like defineNitroConfig and defineNitroPlugin start with define (and Nuxt use defineEventHandler), we could harmonize using defineEventHandler everywhere.

📝 Checklist

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

[nuxt-studio]

✅ Live Preview ready!

Name	Edit	Preview	Latest Commit
nitro	Edit on Studio ↗︎	View Live Preview	180c37f

[codecov]

Codecov Report

Merging #1442 (180c37f) into main (e87e2ba) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1442   +/-   ##
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  Coverage   76.17%   76.17%           
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  Files          73       73           
  Lines        7437     7437           
  Branches      728      728           
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  Hits         5665     5665           
  Misses       1771     1771           
  Partials        1        1           

[Hebilicious]

I like the increased consistency and maybe we should work towards deprecating one of these 2 aliases in h3.

[pi0]

LGTM thanks!