feat: add defaulter for gateway-api resources loading from file

[shawnh2]

What type of PR is this?

What this PR does / why we need it:

• add defaulter for our crd resources, allow them to set default values while loading from file
  • the defaulter code is derived from kubectl-validate's validator, cannot reuse their logic since some of their functions/fields are not exposed
• fix the existing test and add new test for loading supported kind resources

Which issue(s) this PR fixes:

Fixes #4858

Release Notes: Yes

[codecov]

Codecov Report

Attention: Patch coverage is 61.68831% with 59 lines in your changes missing coverage. Please review.

Project coverage is 68.01%. Comparing base (4f01d3f) to head (9eae27e).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/gatewayapi/resource/defaulter.go	62.16%	42 Missing and 14 partials ⚠️
internal/gatewayapi/resource/load.go	50.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5232      +/-   ##
==========================================
+ Coverage   66.91%   68.01%   +1.10%     
==========================================
  Files         211      212       +1     
  Lines       33176    33328     +152     
==========================================
+ Hits        22199    22669     +470     
+ Misses       9628     9290     -338     
- Partials     1349     1369      +20     

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[arkodg]

LGTM thanks !
neat way to default :)

[shawnh2]

/retest