docs: add migration guide

[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)
• ✨ 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

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@nuxt/image@2007

commit: b255980

[cloudflare-workers-and-pages]

Deploying nuxt-image with    Cloudflare Pages

Latest commit:	b255980
Status:	✅  Deploy successful!
Preview URL:	https://278b2819.nuxt-image.pages.dev
Branch Preview URL:	https://docs-release.nuxt-image.pages.dev

View logs

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 7.07%. Comparing base (dfc3ee3) to head (b255980).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##            main   #2007      +/-   ##
========================================
+ Coverage   7.02%   7.07%   +0.05%     
========================================
  Files         77      77              
  Lines       3575    3590      +15     
  Branches     138     139       +1     
========================================
+ Hits         251     254       +3     
- Misses      3276    3288      +12     
  Partials      48      48              

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