[EKS] [request]: Rolling update for managed nodes when updating instance types in combination with spot instances

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**Tell us about your request**
What do you want us to build?

When you have created a node group have the ability to go to eks=>clusters=>your.cluster=>node.group=>edit and change instance types.
So it is possible to have a rolling update for managed nodes using spot configuration when changing instance types.

**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.

I want to be able to change the instance types of a managed node group in combination with spot.
At the moment it is possible to either define 1 instance type via a LT or multiple via node groups.
Tho when you have created the node group there is no option to change the instance types other then changing the ASG created when creating the node groups.
this in turn gives issues when using terraform for example.

**Are you currently working around this issue?**
For now the only option is to create a new node group migrate workload and delete the old node group.

**Additional context**
I came across this issue when testing managed node in combination with terraform. I think the solution provided in this request will allow tools like terraform to allow a rolling updates while also serving users without.
This issue was also partial fixed and discussed in #746 tho it only solved the issue if you use 1 instance type and define it via the LT option

**Attachments**
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Start by reading the request and the referenced issue #746, then clarify how managed node groups, spot configuration, and instance-type changes are expected to interact. The issue is done when users can change instance types for an existing managed node group with spot configuration and perform a rolling update without creating a replacement group.

Written by the indexing model from the issue text.