Allow to [EKS] [request]: Allow r5.8xlarge and r5.12xlarge EC2 instances to be launched in Managed Node group

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**Tell us about your request**
Allow r5.8xlarge and r5.12xlarge EC2 instances to be launched in Managed Node group. Right now it is not possible to select them from console

**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?**
I need to deploy r5.8xlarge and r5.12xlarge as it was required by 3rd party vendor.

**Are you currently working around this issue?**
I am thinking to launch more r5.4xlarge to m5.12xlarge or use self-managed nodes

**Additional context**
Anything else we should know?

**Attachments**
If you think you might have additional information that you'd like to include via an attachment, please do - we'll take a look. (Remember to remove any personally-identifiable information.)

The issue names no repository files, tests, or entry points. Start by reviewing how this roadmap tracks EKS Managed Node Group requests and whether support for r5.8xlarge and r5.12xlarge has moved elsewhere. Done would require maintainer-confirmed support or a documented status for selecting these EC2 instance types.

Written by the indexing model from the issue text.