Enhance docs to include EKS instructions

[ahrkrak]

Current situation We have no instructions for how to make an EKS worker image

Impact Makes it harder and reduces adoption on EKS.

Ideal future situation Docs make it really easy to make an image. We might even want to build an AMI and ship it with each release (maybe via AWS marketplace).

Implementation options See https://aws.amazon.com/de/premiumsupport/knowledge-center/eks-custom-linux-ami/

Additional information [ Please Add any information that does not fit into any of the above sections here ]

[ahrkrak]

Instructions should use Flatcar Pro image from Marketplace.

[pothos]

We have a Terraform setup here: https://github.com/flatcar-linux/flatcar-terraform/tree/main/eks but no section in the docs.