[EKS] [IPv6 on instance TGs]: Add IPv6 support to instance-type target groups for EKS support

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**Tell us about your request**
Please add IPv6 support to instance-type target groups so that we can use EKS cluster autoscaling groups with ALBs/NLBs.

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

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
EKS creates an autoscaling group onto which we can attach target groups; however, the new IPv6-based clusters don't bind NodePorts to the EC2 nodes' IPv4 IPs. We have dual-stack ELBs and IPv6-enabled EKS clusters but seem to be missing that connecting piece in-between.

**Are you currently working around this issue?**
We aren't. We're currently stuck with IPv4 clusters.

**Additional context**
An alternative could be to make EKS clusters dual-stack so we can use the ipFamilies & ipFamilyPolicy features. IPv6-only would be the default to avoid IP exhaustion but we could selectively bind IPv4 IPs as-needed.

**Attachments**
N/A

Start with the issue's description of IPv6-only EKS clusters, instance-type target groups, and dual-stack ELBs. No repository files, tests, or implementation entry points are identified, so first determine where this AWS service behavior is implemented and what acceptance criteria would demonstrate IPv6 support.

Written by the indexing model from the issue text.