This is a follow-up PR for the discussion in original PR- #3315 (comment)

Updates the default release_channel to STABLE

• Current default kueue version is v0.12.4 https://github.com/kubernetes-sigs/kueue/releases/tag/v0.12.4
• The previous need for a non-stable channel was driven by the TopologyAwareScheduling (TAS) feature's beta status. TAS became GA in Kubernetes v1.29.
• Since the GKE STABLE channel now provides Kubernetes v1.30+, which is well beyond the requirement, we can safely and preferably default to STABLE for maximum reliability. https://cloud.google.com/kubernetes-engine/docs/release-notes

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