Hybrid AWS Environments: allow AWS-Auth configuration for IAM roles

At present, GET does not configure appropriate roles for AWS Auth into the EKS cluster.

As a default, EKS will only allow access to the creating user/role.

Other roles should be configurable.

Documentation at: https://docs.aws.amazon.com/eks/latest/userguide/add-user-role.html

(See also linked MRs for implementation details)