Add InstanceOptions with LocalDiskStrategy

[cartermckinnon]

Description of changes:

We've removed the default raid0 setup in #1686, so this adds the ability to setup local disks in NodeConfig.

Example:

---
apiVersion: node.eks.aws/v1alpha1
kind: NodeConfig
spec:
  instance:
    localStorage:
      strategy: RAID0

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[cartermckinnon]

Some kind of issue going on with the conversion-gen check, when I run locally the file has an empty diff 🤔

[cartermckinnon]

Fixed it by adding --output-base to the conversion-gen command. This will default to $GOPATH/src when GOPATH is defined -- it's usually defined on a dev's laptop, but isn't in the GitHub Actions runner.