✨ (go/v4): scaffold kube-api-linter support in new projects

[camilamacedo86]

Summary

• Kubebuilder projects typically scaffold CRD-style APIs, and kube-api-linter exists to enforce those Kubernetes API conventions automatically for CRD authors rather than just core API teams.
• This change wires kube-api-linter directly into the project template: the scaffold now creates a .custom-gcl.yml, adds Makefile and CI hooks, and enables the kubeapilinter module in .golangci.yml so every new operator starts with CRD-focused linting out of the box.
• The optionalfields pointer policy defaults to WhenRequired, matching the kube-api-linter maintainers’ recommendation for CRDs and avoiding the stricter setting that targets core Kubernetes API types (kube-api-linter#128).

Closes: #4809

[k8s-ci-robot]

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This pull-request has been approved by: camilamacedo86

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@camilamacedo86: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kubebuilder-e2e-k8s-1-34-1	2f745c5	link	true	/test pull-kubebuilder-e2e-k8s-1-34-1
pull-kubebuilder-e2e-k8s-1-34-0	ca3b542	link	true	/test pull-kubebuilder-e2e-k8s-1-34-0
pull-kubebuilder-e2e-k8s-1-32-0	ca3b542	link	true	/test pull-kubebuilder-e2e-k8s-1-32-0

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