[EKS] [request]: Option to enable automatic Managed Node Groups AMI version updates

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**Tell us about your request**
I am a heavy user of Managed Node Groups and I want an option to automatically [Update Node Group AMI Version](https://docs.aws.amazon.com/eks/latest/APIReference/API_UpdateNodegroupVersion.html) as new AMI versions become available for the version of Kubernetes the EKS cluster is running.

I want rolling updates to be performed without any manual input from me. When a new AMI version is available, it automatically triggers a rolling update for all node groups attached to the EKS cluster.

**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'm trying to remain as up-to-date as possible with AMI CVEs, patches and improvements. I'm willing to trade stability of bleeding-edge releases for increased security of security patches and OS improvements.

**Are you currently working around this issue?**
I'm having to decide between running my own lambda, my own pod/controller or my own service of some kind that will hit the "UpdateNodegroupVersion" API call on some basis, either scheduled or when there is difference between the latest AMI and the currently running AMI.

**Additional context**
Please allow users to enable fully automatic Managed Node Group AMI updates.

No repository files or tests are identified. Start with the AWS EKS UpdateNodegroupVersion API and determine how an automatic trigger should discover new AMI versions and apply rolling updates to attached managed node groups; done means users can enable fully automatic AMI updates without their own controller or scheduled service.

Written by the indexing model from the issue text.