feat(http): add support for extra headers in serveFile

[moumar]

The headers customization is present in http serveDir but not in serveFile. This PR fixes this.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.14%. Comparing base (76d8c7c) to head (7700f3d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6842   +/-   ##
=======================================
  Coverage   94.13%   94.14%           
=======================================
  Files         577      577           
  Lines       42556    42564    +8     
  Branches     6770     6772    +2     
=======================================
+ Hits        40062    40073   +11     
+ Misses       2442     2440    -2     
+ Partials       52       51    -1     

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[iuioiua]

I think this should be a Headers interface. I also think the same can be said about serveDir.

[kt3k]

The implementation looks good to me. However can you expose headers option only from unstable_file_server.ts for now? (We currently have the policy of not accepting new features directly to stable APIs https://github.com/denoland/std/blob/main/.github/CONTRIBUTING.md#suggesting-a-new-feature )

See how serveDir is exposed in unstable_file_server.ts for reference.

[moumar]

Sounds good to me. Let me update it.