[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
    iam:
      attachPolicyARNs:
        - arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly
        - arn:aws:iam::aws:policy/AmazonEKSWorkerNodePolicy

  - name: generic-2
    iam:
      attachPolicyARNs:
        - arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly
        - arn:aws:iam::aws:policy/AmazonEKSWorkerNodePolicy

  - name: minimal-1
    iam:
      attachPolicyARNs:
        - arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly
        - arn:aws:iam::aws:policy/AmazonEKSWorkerNodeMinimalPolicy

  - name: minimal-2
    iam:
      attachPolicyARNs:
        - arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly
        - arn:aws:iam::aws:policy/AmazonEKSWorkerNodeMinimalPolicy

[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

  minimalAttachPolicyARNs: &minimalAttachPolicyARNs
  - arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly
  - arn:aws:iam::aws:policy/AmazonEKSWorkerNodeMinimalPolicy

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

managedNodeGroups:
  - name: generic-1
    iam:
      attachPolicyARNs: *genericAttachPolicyARNs

  - name: generic-2
    iam:
      attachPolicyARNs: *genericAttachPolicyARNs

  - name: minimal-1
    iam:
      attachPolicyARNs: *minimalAttachPolicyARNs

  - name: minimal-2
    iam:
      attachPolicyARNs: *minimalAttachPolicyARNs