aws: plumb enable_aws_load_balancer_controller_pod_identity through to the EKS module

[dcmcand]

Surfaced during review of #259 (pkg/provider/aws/templates/main.tf).

The upstream terraform-aws-eks-cluster module exposes an enable_aws_load_balancer_controller_pod_identity variable that gates creation of the IAM role and Pod Identity association used by the LBC. We do not currently pass that variable from NIC, so users who set aws_load_balancer_controller.enabled: false still get an unused IAM role and Pod Identity association provisioned.

Proposed fix

Pass the value of aws_load_balancer_controller.enabled through to enable_aws_load_balancer_controller_pod_identity in pkg/provider/aws/templates/main.tf, and surface it as a Terraform variable from the Go config.

Definition of done

• enable_aws_load_balancer_controller_pod_identity is wired through from config
• Disabling LBC results in no IAM role or Pod Identity association being created
• Unit test for variable generation covers both states
• Example config / docs updated to mention the resource implication

Review thread: #259 (comment)