feat: support base in useStorage(base?: string) and improve docs

[atinux]

🔗 Linked issue

Resolves #1008

❓ 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

Support useStorage(base) as well as improving the documentation about storage.

📝 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	671b02f

[atinux]

I added tests but I am struggling to make them work, no idea what is the signature of callhandler() 😬

[codecov]

Codecov Report

Merging #1012 (0209224) into main (a615444) will increase coverage by 0.03%.
The diff coverage is 100.00%.

❗ Current head 0209224 differs from pull request most recent head 671b02f. Consider uploading reports for the commit 671b02f to get more accurate results

@@            Coverage Diff             @@
##             main    #1012      +/-   ##
==========================================
+ Coverage   67.66%   67.69%   +0.03%     
==========================================
  Files          60       60              
  Lines        6161     6167       +6     
  Branches      692      692              
==========================================
+ Hits         4169     4175       +6     
  Misses       1982     1982              
  Partials       10       10              

Impacted Files	Coverage Δ
src/rollup/plugins/storage.ts	98.76% <100.00%> (+0.09%)	⬆️

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