eksctl create nodegroup on an outdated cluster stack template fails if subnets are missing

[cPu1]

Part of #7714, when creating a nodegroup whose cluster's stack template is missing resources added since eksctl last updated the template, eksctl will attempt to update the cluster's stack to add missing resources. However, if the cluster's stack has subnets (and other resources) that no longer exist (e.g., if they were deleted outside eksctl), the CloudFormation stack update will fail.

However, very few users would run into this issue as the cluster's stack template has not been updated in a long time.

[github-actions]

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