kubectl convert was removed in 1.20

[sotoiwa]

Describe the problem
kubectl convert was removed in 1.20 and is now available as a plugin for kubectl. I think the link and description need to be updated.

kubernetes/kubectl#725
https://kubernetes.io/docs/tasks/tools/included/kubectl-convert-overview/
https://kubernetes.io/docs/tasks/tools/install-kubectl-linux/#install-kubectl-convert-plugin

References
https://aws.github.io/aws-eks-best-practices/reliability/docs/controlplane/#handling-cluster-upgrades

[realvz]

Thanks @sotoiwa, again :). I have updated the doc to mention that kubectl convert is now a plugin.