cannot change EKS cluster encryption config without replacement

### Name of the resource

AWS::EKS::Cluster

### Resource Name

_No response_

### Issue Description

Reopening #1234. The response that you "do not have a plan to support updating encryption config" is not acceptable.

EKS supports enabling (but not disabling) secret encryption on an existing cluster. https://docs.aws.amazon.com/eks/latest/userguide/enable-kms.html

However, attempting to enable encryption via CloudFormation will force a replacement for no reason. https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-eks-cluster.html#cfn-eks-cluster-encryptionconfig

### Expected Behavior

Enabling encryption on an existing cluster via CloudFormation must be allowed.

### Observed Behavior

CloudFormation forces a cluster replacement for no reason.

### Test Cases

Create an EKS cluster with encryption disabled. Then update the stack to enable it.

### Other Details

_No response_

Start with the AWS::EKS::Cluster resource documentation and reproduce the stated update: create a cluster without encryption, then enable encryption in the stack. Done means CloudFormation permits enabling encryption on the existing cluster without replacement; the issue does not name source files or tests.

Written by the indexing model from the issue text.