Ability to manage EKS aws-auth configmap from CloudFormation

### Name of the resource

AWS::EKS::Cluster

### Resource name

_No response_

### Description

We need a way to add role and user mappings in the aws-auth configmap via CloudFormation. This would allow us to bridge the IAM to Kubernetes RBAC divide at cluster creation time. Ideally, it would manage entries individually, and would not disturb configuration added manually.

### Other Details

_No response_

Start by reviewing the AWS::EKS::Cluster resource and the EKS aws-auth ConfigMap behavior. Define how individual role and user mappings would be managed at cluster creation while preserving entries added manually; done means CloudFormation can maintain those mappings without disturbing existing configuration.

Written by the indexing model from the issue text.