[EKS] [request]: Support pause/termination in Managed Nodegroup update workflow

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**Tell us about your request**
Once the nodegroup updation workflow starts, there is no way of pausing/terminating the same if we realize we have made an errorneous update midway through the workflow.

**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 might find something going wrong when updating and want to make sure the update isn't causing it, so a way to pause the upgrade would be nice. Same goes for being able to terminate the update workflow.

**Are you currently working around this issue?**
N/A

**Additional context**
N/A

**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.)

Start by reviewing the EKS managed nodegroup update workflow and how an in-progress update is represented. Define how users would pause or terminate an update, including its observable outcome; the work is done when both controls behave predictably during an update.

Written by the indexing model from the issue text.