archive: add gitea generic package registry backend

[mahaase]

Add a gitea archive backend that stores binary artifacts in a Gitea generic package registry. The backend is configured with the server url, the registry owner and the generic package name. Credentials are given explicitly as a token (personal access token) or a user/password pair for HTTP basic authentication, so uploads work even inside the build sandbox. Optional sslVerify and retries keys tune the transport.

Uploads perform a preflight check and report clearer connection and authentication errors.

• archive: implement the gitea backend with upload preflight and clearer connection/auth error reporting
• input: validate the gitea archive backend configuration
• doc: document the gitea archive backend
• test: cover the gitea archive backend

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.35%. Comparing base (7b00892) to head (fe1828f).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #705      +/-   ##
==========================================
+ Coverage   89.23%   89.35%   +0.12%     
==========================================
  Files          50       50              
  Lines       16450    16614     +164     
==========================================
+ Hits        14679    14846     +167     
+ Misses       1771     1768       -3     

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[mahaase]

i'm not sure, but the root cause of the failed windows build could be:
Error: Failed to download: [Errno 28] Disk full