[EKS] [request]: Create a notification for new versions of the EKS Optimized AMI

### Community Note

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**Tell us about your request**
What do you want us to build?
Create an SNS topic for notifying customer when a new version of the EKS Optimized AMI is available.

**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?**
What outcome are you trying to achieve, ultimately, and why is it hard/impossible to do right now? What is the impact of not having this problem solved? The more details you can provide, the better we'll be able to understand and solve the problem.
Today, you have to call an API to upgrade the worker nodes in a managed node group. A notification would tell customer when a new version is available for upgrade.

**Are you currently working around this issue?**
How are you currently solving this problem?
Customers can monitor the GitHub repository, e.g. https://help.github.com/en/github/receiving-notifications-about-activity-on-github/watching-and-unwatching-releases-for-a-repository.

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

**Attachments**
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