Add EKS support to VPC module
This MR allows the user to enable EKS support, so that EKS clusters can share a pre-existing VPC in a non-destructive way. Tested within Radio.co's staging environment with success.
For further testing, it'd be useful to attempt a terraform plan against this branch in another account/environment.
Desired effect is extra tags when EKS is enabled, and no change when not enabled.
New variables for this module are enable_eks_support = "true|false" and eks_cluster_name = "string". Both variables are string types.