feat: Add new IAM module iam-eks-role

[max-rocket-internet]

Description

Adding a new, user-friendly module that is specifically for AWS EKS users.

Motivation and Context

Currently EKS users would use the module iam-assumable-role-with-oidc but the way it is structured/implemented is quite confusing:

1. You have to deal with or know your cluster OIDC URL
2. Can't create a role that is assumable by multiple ServiceAccount per multiple clusters as provider_urls and oidc_fully_qualified_subjects are separate.
3. Most EKS users don't know what oidc_fully_qualified_subjects are and shouldn't need to.
4. It still needs to be wrapped in another module or requires a data resource to get the OIDC URL of each cluster

This module solves these in a nice clean way for EKS users by using a data resource inside the module and having a one-to-many relationship from provider_url to oidc_fully_qualified_subjects but implemented simply as EKS cluster name to ServiceAccount, like this:

module "iam_eks_role" {
  source    = "terraform-aws-modules/iam/aws//modules/iam-eks-role"
  role_name = "my-app"

 cluster_service_accounts = {
    "cluster-main-1" = [
      "default:my-app-staging",
      "canary:my-app-staging"
    ]
    "cluster-backup-1" = [
      "default:my-app-staging",
    ]
  }

Breaking Changes

It's a new module so no breaking changes.

How Has This Been Tested?

• I have tested and validated these changes using one or more of the provided examples/* projects.
• I have also tested this in our environment

[antonbabenko]

Looks pretty good to me. Minor comments.

[antonbabenko]

And remove version

[max-rocket-internet]

Thanks for the review @antonbabenko! I think I've addressed everything 🙏

[antonbabenko]

This PR is included in version 4.9.0 🎉

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