Support node-level user namespace remapping

**Tell us about your request**
Support user namespace remapping to map root inside container to non-root on host. This is good feature for container security, and give better protection against Worker Node. However it is not implemented by upstream yet, would like to know if AWS can add it to EKS.

KEP: https://github.com/kubernetes/community/pull/2067

Enhancement issue: https://github.com/kubernetes/enhancements/issues/127

@mhausenblas pls check

Start with the linked Kubernetes KEP and enhancement issue to understand the proposed user namespace remapping design and its upstream status. Confirm whether upstream support exists before assessing EKS implementation; done would mean AWS documents or delivers support for mapping container root to a non-root host identity.

Written by the indexing model from the issue text.