Reapply "Merge pull request #10069 from Turbo87/publish-stream"

[Turbo87]

This reverts commit 4f55cbe.

The AWS team has investigated and fixed the Cloudfront issue that led to early responses being converted to HTTP 5xx errors on their side, so this refactoring can be applied again :)

Related:

• controllers/krate/publish: Validate JSON metadata before reading tarball #10069
• 503 on publishing a crate #10098
• Revert "Merge pull request #10069 from Turbo87/publish-stream" #10102

[codecov]

Codecov Report

Attention: Patch coverage is 92.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 89.57%. Comparing base (0aea38a) to head (6e71d80).
Report is 18 commits behind head on main.

Files with missing lines	Patch %	Lines
src/controllers/krate/publish.rs	87.09%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10166      +/-   ##
==========================================
- Coverage   89.57%   89.57%   -0.01%     
==========================================
  Files         295      295              
  Lines       31690    31720      +30     
==========================================
+ Hits        28386    28412      +26     
- Misses       3304     3308       +4     

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