ci: updating kustomize to 5.6.0

[JaydipGabani]

What this PR does / why we need it:

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[Copilot]

Pull Request Overview

This PR updates the Kustomize version from 3.8.9 to 5.6.0 to leverage newer features and improvements. The update requires migrating all kustomization.yaml files to explicitly declare API version and Kind fields, and to use updated field names and patch syntax that are compatible with Kustomize v5.6.0.

• Updated Kustomize version from 3.8.9 to 5.6.0 in Makefile
• Migrated kustomization.yaml files to declare explicit apiVersion: kustomize.config.k8s.io/v1beta1 and kind: Kustomization
• Replaced deprecated patchesStrategicMerge, patchesJson6902, bases, and commonLabels with modern equivalents (patches, resources, labels)
• Updated Makefile command flag from --load_restrictor to --load-restrictor

Reviewed Changes

Copilot reviewed 42 out of 42 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Makefile	Updated KUSTOMIZE_VERSION to 5.6.0 and changed command flag to use hyphenated format
config/*/kustomization.yaml	Added apiVersion and kind fields, migrated from deprecated syntax to modern Kustomize v5 syntax
cmd/build/helmify/kustomization.yaml	Restructured to use modern patches format and explicit API version declaration
manifest_staging/deploy/gatekeeper.yaml	Auto-generated formatting changes to YAML descriptions (line wrapping)
manifest_staging/charts/gatekeeper/templates/*.yaml	Deleted files (likely regenerated by tooling)
manifest_staging/charts/gatekeeper/crds/*.yaml	Deleted files (likely regenerated by tooling)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 40.68%. Comparing base (3350319) to head (18c0fbd).
⚠️ Report is 471 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (3350319) and HEAD (18c0fbd). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (3350319)	HEAD (18c0fbd)
unittests	2	1

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4198       +/-   ##
===========================================
- Coverage   54.49%   40.68%   -13.82%     
===========================================
  Files         134      251      +117     
  Lines       12329    17720     +5391     
===========================================
+ Hits         6719     7209      +490     
- Misses       5116     9887     +4771     
- Partials      494      624      +130     

Flag	Coverage Δ
unittests	40.68% <ø> (-13.82%)	⬇️

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