fix: add CORS to config, improve test

[fetsorn]

Hotfix for #516, I've corrected the test case and added CORS to the default config.

• prepend c.HTTP.PublicURL to c.HTTP.CORS.AllowedOrigins in the Config.Validate() function.
• make the testscript case more readable
• hint a custom allowed origin in the config
• enable PUT and OPTIONS in default config

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.76%. Comparing base (b06b555) to head (4941bcd).
Report is 136 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #654      +/-   ##
==========================================
- Coverage   51.96%   51.76%   -0.20%     
==========================================
  Files         157      159       +2     
  Lines       13454    13569     +115     
==========================================
+ Hits         6991     7024      +33     
- Misses       5891     5973      +82     
  Partials      572      572              

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[aymanbagabas]

Thank you for the changes @fetsorn! I will merge once the tests pass

[fetsorn]

I also added several allowed headers needed for preflight requests