[eks] [request]: Support surging updates for MNGs

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**Tell us about your request**
I'd like EKS Managed Node Groups (MNGs) to have an option to surge when updating instead of needing to terminate an instance before adding a new one. This would make the new compute capacity be available before any terminations so pod have somewhere to be re-scheduled.

**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?**
When updating MNGs we regularly see issues caused by a lack of capacity for terminated pods to run on, this is a major issue when running stateful workloads across AZs with PDBs (K8s best practice).

**Are you currently working around this issue?**
I can't use MNGs while this behaviour isn't supported.

**Additional context**
See #1865

**Attachments**
n/a

The request concerns EKS Managed Node Groups and references related issue #1865. Start by reading #1865 and the request details to define how surge behavior should work; done means MNG updates can add replacement capacity before terminating existing instances, including for stateful workloads with PDBs.

Written by the indexing model from the issue text.