refactor: add gatewayapi/resource pkg

[shawnh2]

What type of PR is this?

What this PR does / why we need it:

• move gatewayapi/resource.go into gatewayapi/resource/*
• move gatewayapi/translator.go's kind into gatewayapi/resource/*
• move shared kubernetesYAMLToResources func into gatewayapi/resource/*

Which issue(s) this PR fixes:

This is a refactor PR before implementing #1295, and it's very likely to get conflicts, so should be reviewed ASAP.

[codecov]

Codecov Report

Attention: Patch coverage is 26.16984% with 426 lines in your changes missing coverage. Please review.

Project coverage is 65.65%. Comparing base (14f687f) to head (bb107ef).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/gatewayapi/resource/load.go	0.00%	333 Missing ⚠️
internal/provider/kubernetes/controller.go	38.46%	24 Missing ⚠️
internal/cmd/egctl/status.go	0.00%	13 Missing ⚠️
internal/provider/kubernetes/routes.go	0.00%	12 Missing ⚠️
internal/provider/kubernetes/status_updater.go	14.28%	12 Missing ⚠️
internal/gatewayapi/validate.go	72.00%	3 Missing and 4 partials ⚠️
internal/provider/file/resources.go	0.00%	6 Missing ⚠️
internal/provider/file/store.go	0.00%	5 Missing ⚠️
internal/provider/kubernetes/helpers.go	0.00%	3 Missing ⚠️
internal/provider/kubernetes/indexers.go	83.33%	3 Missing ⚠️
... and 6 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4235      +/-   ##
==========================================
- Coverage   66.50%   65.65%   -0.86%     
==========================================
  Files         195      196       +1     
  Lines       23732    23538     -194     
==========================================
- Hits        15783    15453     -330     
- Misses       6831     6976     +145     
+ Partials     1118     1109       -9     

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[arkodg]

SGTM

[zirain]

/retest