Simplified: Fix Header Parsing

[wolveix]

Previously, the findHeaders func ignored structs as headers were intended to only be set at the top-level of the output struct. This worked; however, there was a subtle bug within _findInType that meant this was ignored if a field was a struct slice (or array, or map) rather than just a single struct.

This introduced various issues, namely the documentation and setting of headers from struct slices, which was particularly problematic for []*http.Cookie. This fix adjusts the struct type detection to automatically detect arrays, maps, and slices and check their root type.

This PR also implements support for hidden headers (nested or otherwise) from the generated OpenAPI documentation.

This PR:

• Fixes Applying common headers to multiple responses (docs issue) #480 by supporting hiding headers from OpenAPI documentation
• Fixes Docs UI doesn't handle multiple cookies properly #403 and Serialization of []http.Cookie is wrong #776 by not setting headers based on struct slice fields

---

I created this as an improved and simplified version of #943 which doesn't require recursive field resolution. This means it doesn't close as many issues as it doesn't implement new functionality, but does resolve a few bugs.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.62%. Comparing base (1cd5c26) to head (2075587).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #944      +/-   ##
==========================================
+ Coverage   92.54%   92.62%   +0.07%     
==========================================
  Files          23       23              
  Lines        4481     4499      +18     
==========================================
+ Hits         4147     4167      +20     
+ Misses        275      274       -1     
+ Partials       59       58       -1     

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