feat: new github provider

[luc122c]

🔗 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

This PR adds a new image provider: GitHub. This provider is purely for user's avatar images.

This is an extension of this PR in the nuxters repo. After messaging @danielroe I've brought the provider across into the main nuxt/image repo. I've made some small changes to satisfy the TypeScript compiler.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@nuxt/image@1990

commit: 18ee298

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 7.03%. Comparing base (4de3656) to head (18ee298).
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
src/runtime/providers/github.ts	0.00%	21 Missing and 1 partial ⚠️
src/provider.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main   #1990      +/-   ##
========================================
- Coverage   7.08%   7.03%   -0.05%     
========================================
  Files         76      77       +1     
  Lines       3529    3552      +23     
  Branches     137     138       +1     
========================================
  Hits         250     250              
- Misses      3232    3254      +22     
- Partials      47      48       +1     

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