Move to managed IAM policy for awslb service account for testbed addon.

Testbed:

Either moved to a managed policy like `AWSLoadBalancerControllerIAMPolicy` when it's available in IAM (or) scope down the policies of AWS LB IRSA role using this - https://raw.githubusercontent.com/kubernetes-sigs/aws-load-balancer-controller/v2.2.0/docs/install/iam_policy.json

Start by locating the testbed addon and the awslb service account configuration. Compare its AWS LB IRSA permissions with the referenced AWS Load Balancer Controller IAM policy and determine whether the managed policy is available in IAM. Done means the addon uses the managed policy, or the IRSA role is scoped to the required permissions.

Written by the indexing model from the issue text.