feat: allow custom global options for $fetch.create

[CafuChino]

🔗 Linked issue

#71

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 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)
• 🧹 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 commit adds an optional parameter globalOptionsOverwrite to $fetch.create.

However, for HTTP, headers are not case-sensitive. But for some reason, headers are case-sensitive in some old backend frameworks. This optional parameter overrides native Headers behaviour in such situations.

As only adding an optional parameter, it won`t break anything, maybe?

📝 Checklist

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.22%. Comparing base (27996d3) to head (8ff591b).
Report is 36 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #401       +/-   ##
===========================================
+ Coverage   56.86%   67.22%   +10.35%     
===========================================
  Files          16       16               
  Lines         728      476      -252     
  Branches      113      116        +3     
===========================================
- Hits          414      320       -94     
+ Misses        303      146      -157     
+ Partials       11       10        -1     

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[pi0]

LGTM. Although modifying standard globals should be last resort, there are legitimate usecases and it is better than patching actual globals