[EKS] [request]: Add/Remove Availability Zone(AZ) for Worker Nodes during EKS Cluster Dataplane Upgrade

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**Tell us about your request**
Add/Remove Availability Zone(AZ) for Worker Nodes during EKS Cluster Dataplane Upgrade

**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?**
The ability to expand the number of Availability Zones (AZ) for the Dataplane (Worker Nodes) Node Group while upgrading the Cluster. Clients seeking more IP capacity for worker nodes and high availability may wish to add or remove the extra AZ. We urgently need to have this feature available for customer needs as AWS EKS does not currently offer it.

**Are you currently working around this issue?**
We are unable to resolve this problem during Cluster upgrade scenarios.

No source files, tests, or implementation entry points are identified. Start by reviewing the EKS dataplane upgrade and worker-node Availability Zone behavior described in the request; done would mean a delivered capability that supports adding and removing AZs during an upgrade.

Written by the indexing model from the issue text.