[EKS] [request]: toggleable aws-auth roleArn deletion for managed node groups

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**Tell us about your request**
Make toggleable aws-auth roleArn deletion for managed node groups

**Which service(s) is this request for?**
EKS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
Currently if we create a managed node group and an unmanaged set of nodes that use the same roleArn, then deletion of the managed node group will remove the roleArn that is still in use by the unmanaged nodes. This orphans the unmanaged nodes and would require the user to add the roleArn back in. It would be nice to allow infrastructure as code software like terraform or eksctl to manage it instead since it has an overall view of nodes that are deployed.

**Are you currently working around this issue?**
Manually adding the aws-auth roleArn entry back in

**Additional context**

**Attachments**

Start by reviewing the EKS managed node group deletion behavior described here, focusing on the aws-auth roleArn entry shared with unmanaged nodes. Compare how Terraform or eksctl could control this behavior, and consider the request complete when roleArn deletion can be toggled without orphaning still-active unmanaged nodes.

Written by the indexing model from the issue text.