fix: handle shorthand_field defaults in skip-defaults dump

[Prashansa-K]

Summary

shorthand_fields don't have defaults defined in the schema.
Thus, while using deck gateway dump --skip-defaults, they still show up.
This fix handles shorthand_fields by checking their default values against
their new fields represented by replaced_with or translate_backwards in the schema.

Tested here in deck: Kong/deck#1810

Issues resolved

For Kong/deck#1808

Documentation

• Link to the website documentation PR

Testing

• Unit tests
• E2E tests
• Manual testing on Universal
• Manual testing on Kubernetes

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.33333% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 29.05%. Comparing base (e412658) to head (2dc1c40).

Files with missing lines	Patch %	Lines
pkg/dump/skip_defaults.go	83.33%	5 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #357      +/-   ##
==========================================
+ Coverage   28.87%   29.05%   +0.18%     
==========================================
  Files         119      119              
  Lines       16138    16192      +54     
==========================================
+ Hits         4660     4705      +45     
- Misses      10859    10864       +5     
- Partials      619      623       +4     

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