Move Pod group labels and annotations to apis/ package

[PBundyra]

What would you like to be added:
Move consts

GroupNameLabel               = "kueue.x-k8s.io/pod-group-name"
GroupTotalCountAnnotation    = "kueue.x-k8s.io/pod-group-total-count"
GroupFastAdmissionAnnotation = "kueue.x-k8s.io/pod-group-fast-admission"
RoleHashAnnotation           = "kueue.x-k8s.io/role-hash"
RetriableInGroupAnnotation   = "kueue.x-k8s.io/retriable-in-group"

from pkg/controller/jobs/pod/pod_webhook.go to apis package

Why is this needed:
To improve code quality and API visibility

[tenzen-y]

I think that we should not move those labels to apis package since those are not for a whole of Kueue projects.

Instead of that, I think that creating dedicated constants package or restructure the Pod, Deployment, and StatefulSet packages. For example, we might be able to restructure those packages based on the Pod directory.

This is a similar concept to KubeflowJobs.

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/lifecycle stale

[PBundyra]

/remove-lifecycle stale