[self-hosted/docs] update reference architecture Kubernetes versions to track updates

[adrienthebo]

Is your feature request related to a problem? Please describe

At present the EKS and GKE installation guides use hardcoded Kubernetes versions when creating the underlying Kubernetes clusters. While eksctl accepts a Kubernetes version number that will pick up the latest patch release (eg 1.22) a better mechanism is needed to ensure that the reference architecture version stays current.

Describe the behaviour you'd like

The reference architecture Kubernetes version should feature install instructions that install the latest supported version of Kubernetes on the given cloud platform.

[stale]

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