[Feature] ClusterConfig to support for YAML anchors and aliases

[guessi]

What feature/behavior/change do you want?

By current design, eksctl not able to accept ClusterConfig with YAML anchors or aliases. If there have any unsupported entry, it would emit error as follow,

Error: couldn't create node group filter from command line options: loading config file "./clusterConfig.yaml": error unmarshaling JSON: while decoding JSON: json: unknown field "aliases"

Why do you want this feature?

If ClusterConfig could support YAML anchors or aliases, we could turn [1] to [2].

What is the workaround for this feature?

yq -y 'del(.aliases)' ./clusterConfig.yaml | eksctl create nodegroup --dry-run -f  -

Reference YAMLs:

[1] BEFORE

---
apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig

metadata:
  name: eks-demo
  region: us-east-1

managedNodeGroups:
  - name: generic-1
    minSize: 2
    maxSize: 5
    desiredCapacity: 2
    volumeSize: 30
    volumeType: gp3
    instanceTypes:
    - "t3a.small"
    - "t3.small"
    iam:
      attachPolicyARNs:
        - arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly
        - arn:aws:iam::aws:policy/AmazonEKSWorkerNodePolicy

  - name: generic-2
    minSize: 2
    maxSize: 5
    desiredCapacity: 2
    volumeSize: 30
    volumeType: gp3
    instanceTypes:
    - "t3a.small"
    - "t3.small"
    iam:
      attachPolicyARNs:
        - arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly
        - arn:aws:iam::aws:policy/AmazonEKSWorkerNodePolicy

[2] AFTER

---
apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig

aliases: # By current design, it would cause template parsing error
  genericAttachPolicyARNs: &genericAttachPolicyARNs
  - arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly
  - arn:aws:iam::aws:policy/AmazonEKSWorkerNodePolicy

  genericNodeGroupSettings: &genericNodeGroupSettings
    minSize: 2
    maxSize: 5
    desiredCapacity: 2
    volumeSize: 30
    volumeType: gp3
    instanceTypes:
    - "t3a.small"
    - "t3.small"
    enableDetailedMonitoring: true
    privateNetworking: true
    disableIMDSv1: true
    spot: true
    ssh:
      allow: false

metadata:
  name: eks-demo
  region: us-east-1

managedNodeGroups:
  - name: generic-al2
    amiFamily: AmazonLinux2
    <<: *genericNodeGroupSettings
    iam:
      attachPolicyARNs: *genericAttachPolicyARNs

  - name: generic-al2023
    amiFamily: AmazonLinux2023
    <<: *genericNodeGroupSettings
    iam:
      attachPolicyARNs: *genericAttachPolicyARNs

[github-actions]

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