[EKS] [request] masters/etcd snapshots

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**Tell us about your request**
Ability to snapshot the masters/etcd and restore. The intended use case is to allow rollback for cluster upgrades. But could also be useful for any corruption.

**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?**
Supporting rollbacks for example when a cluster is upgraded from 1.14 to 1.15 a path to rollback would be useful.

**Are you currently working around this issue?**
No, only mitigating the risk by testing upgrades on ephemeral test clusters.

**Additional context**
I searched issues but only could find #404 which is more specific and relates to backing up at the namespace level. I expect my request might be a simpler implementation and something you do today but don’t expose to customers.