[EKS] [request]: Support configuring default Docker credentials for EKS nodes

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**Tell us about your request**
Our team would like to avoid the [Docker pull rate limit](https://www.docker.com/increase-rate-limits) by authenticate with Docker hub on every EKS node.

**Which service(s) is this request for?**
EKS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
We were exceeding the anonymous pull rate limit for Docker Hub which prevented some of our containers from starting up, so we would like to authenticate with Docker Hub on every node. We are aware of a few workarounds for this issue, e.g. using a userdata script to configure Docker on startup or configure `ImagePullSecrets` for namespaces or service accounts. The userdata approach seems closest to what we want but ideally we would like to configure the default Docker credentials as part of node group or cluster configuration.

**Are you currently working around this issue?**
Yes, we are using a custom userdata script in the launch configuration to authenticate with Docker hub on each node.

**Additional context**
- Kops supports this https://github.com/kubernetes/kops/blob/release-1.8/docs/security.md#docker-configuration

**Attachments**
N/A

Start by reviewing the EKS node group or cluster configuration entry points and the launch configuration's custom userdata approach described in the issue. Compare that with ImagePullSecrets and the cited kops Docker configuration, then define completion as a supported configuration that authenticates every EKS node with Docker Hub without a custom userdata script.

Written by the indexing model from the issue text.