Default HorizontalPodAutoscaler to autoscaling/v2

What does this MR do?

Defaults the HorizontalPodAutoscaler apiVersion to autoscaling/v2.

When the chart is rendered without cluster API discovery (for example helm template without --api-versions, as common in GitOps pipelines), the HPA apiVersion fell back to autoscaling/v2beta1, which was removed in Kubernetes 1.25. That also meant offline renders silently dropped behavior and used v2beta1-style metric targets. Every Kubernetes version the chart supports (1.34+) serves autoscaling/v2, so this makes it the default and drops the autoscaling/v2beta2 capability probe.

Explicit global.hpa.apiVersion and local hpa.apiVersion overrides are unchanged, and the v2beta1/v2beta2 metric-spec handling stays in place for anyone who sets them explicitly.

Also fixes the "HoritonzalPodAutoscaler" typo in the helper comment.

It also removes the now-redundant global.hpa.apiVersion: autoscaling/v2 pin from HELM_DEFAULT_SETTINGS in .gitlab-ci.yml, so the kubeconform and template check jobs exercise the new default.

Verification: helm template renders all 5 default HPAs as autoscaling/v2; --set global.hpa.apiVersion=autoscaling/v2beta2 still renders autoscaling/v2beta2. RSpec was not run locally (no suitable Ruby available); relying on CI for spec/configuration/hpa_spec.rb.

Kubernetes references:

• autoscaling/v2beta1 is no longer served as of Kubernetes 1.25: Deprecated API Migration Guide – HorizontalPodAutoscaler v1.25
• autoscaling/v2beta2 is no longer served as of Kubernetes 1.26: Deprecated API Migration Guide – HorizontalPodAutoscaler v1.26
• Announcement: Kubernetes Removals, Deprecations, and Major Changes in 1.26

Related issues

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