[EKS] Managed NodeGroups: option to enable activity notifications on autoscaling group

**What do you want us to build?**

Add an option on the managed node group to enable activity notifications to be sent to an SNS topic. This setting is on the ASG that is created by the managed node group. API reference is [here](https://docs.aws.amazon.com/autoscaling/ec2/APIReference/API_PutNotificationConfiguration.html)

**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?**

We want send ASG activity notifications to SNS so we can log/filter/parse them externally.

**Are you currently working around this issue?**

How are you currently solving this problem?

We aren't as it's not possible to enable this setting.

Start with the issue's AWS PutNotificationConfiguration API reference and the EKS managed node group documentation. Determine where the option belongs and how it should configure the node group's Auto Scaling Group; done means activity notifications can be sent to the requested SNS topic.

Written by the indexing model from the issue text.