Update aws-auth configmap documentation

**Describe the problem**
The aws-auth configmap documentation needs an update, now that the Cluster Access Manager API has been added and is the preferred way to manage access of AWS IAM principals to Amazon EKS clusters.

Content to update:
* https://github.com/aws/aws-eks-best-practices/blob/master/content/reliability/docs/controlplane.md
* https://github.com/aws/aws-eks-best-practices/blob/master/content/security/docs/detective.md
* https://github.com/aws/aws-eks-best-practices/blob/master/content/security/docs/iam.md

The new Cluster Access Manager is mentioned in `iam.md` but there is a lot of old and possibly obsolete information preceding it. Suggestion: Move the `aws-auth` paragraph to the bottom and add a disclaimer.

The User Guide can also use an update. A lot of docs point to the following, which is now essentially obselete:

https://docs.aws.amazon.com/eks/latest/userguide/add-user-role.html#aws-auth-configmap

Users should be directed to the following instead?

https://docs.aws.amazon.com/eks/latest/userguide/access-entries.html

**References**
* https://aws.amazon.com/blogs/containers/a-deep-dive-into-simplified-amazon-eks-access-management-controls/
* https://github.com/aws/containers-roadmap/issues/185#issuecomment-1863025784

Start by reading content/reliability/docs/controlplane.md, content/security/docs/detective.md, and content/security/docs/iam.md, then compare their aws-auth guidance with the referenced EKS access-entries User Guide. Update obsolete guidance and links so Cluster Access Manager is presented as the preferred approach, with aws-auth clearly qualified as legacy; review all three pages for consistent wording.

Written by the indexing model from the issue text.