Document strategy to do something like "get k8s version" once for each cluster

[consideRatio]

This is examplified in #3224, but not documented as a generally useful strategy for misc things yet. We should document that!

[consideRatio]

Here is a fresh example of doing this where we rely on deployer config get-clusters --provider=gcp to get all GCP clusters for example.

deployer config get-clusters --provider=gcp | xargs -I {} deployer use-cluster-credentials {} 'echo {} && kubectl get cm -n kube-system -o yaml calico-typha-horizontal-autoscaler | yq eval ".data.ladder" - | yq eval ".nodesToReplicas[1]" -'