Don't create a new Security Group for EKS cluster if it's only used with Managed Node Groups

[aknysh]

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Describe the Feature

• Don't create a new Security Group for EKS cluster if it's used with Managed Node Groups

Describe Ideal Solution

We need to create a new Security Group only if the EKS cluster is used with unmanaged worker nodes.
EKS creates a security group for the cluster, places the control plane and managed nodes into the security group, and allows all communications between the control plane and the managed worker nodes.
If only Managed Node Groups are used, we don't need to create a separate Security Group; otherwise we place the cluster in two SG - one that is created by EKS, the other that the module creates.

See https://docs.aws.amazon.com/eks/latest/userguide/sec-group-reqs.html for more details.