update deprecated APIs in 1.19 manifests

[mboersma]

Describe the request
Several Kubernetes APIs were deprecated in the 1.19.0-alpha.3 release:
https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG/CHANGELOG-1.19.md#deprecation

Specifically:

Deprecated	1.19+
apiextensions.k8s.io/v1beta1	apiextensions.k8s.io/v1
apiregistration.k8s.io/v1beta1	apiregistration.k8s.io/v1
authentication.k8s.io/v1beta1	authentication.k8s.io/v1
autoscaling/v2beta1	autoscaling/v2beta2
coordination.k8s.io/v1beta1	coordination.k8s.io/v1
storage.k8s.io/v1beta1	storage.k8s.io/v1

I began making these changes to the 1.19 manifests in the 1.19.0-alpha.3 PR (#3197) but quickly realized:

• this change presumably isn't urgent, it's just getting out ahead of the deprecations
• such changes will be much more rational after consolidate addons specs in single files #3188 is complete

Explain why AKS Engine needs it

Describe the solution you'd like
Adding some go template code to the unified manifests after #3188 is completed, to change these API versions depending on Kubernetes version in a self-documenting way:

{{- if IsKubernetesVersionGe "1.19.0-alpha.3"}}
apiVersion: apiextensions.k8s.io/v1
{{else}}
apiVersion: apiextensions.k8s.io/v1beta1
{{- end}}

Describe alternatives you've considered

Additional context

[stale]

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