[EKS] [request]: Managed Node Groups - Ability to modify subnets of underlying ASG

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**Tell us about your request**
Currently, EKS managed node group cannot update the network configuration after the node group has been created. When there is a need to update the node groups to use new subnets, it cannot be done.

It will be more convenience if we can directly update the subnet configuration from EKS console/API similar to the way we can modify subnets for an Auto Scaling Group.

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

**Are you currently working around this issue?**
Currently limited to use the subnets provided during creation.

This is a public roadmap request rather than a code-scoped task. Start by reviewing how EKS managed node groups expose network configuration through the EKS console/API and how their underlying Auto Scaling Groups use subnets. Done means users can update a node group’s subnet configuration after creation without recreating it.

Written by the indexing model from the issue text.