terraform-provider-constellation: make kubeconfig output fine-grained

[msanft]

Context

To directly plug in the Constellation Terraform provider into the kubernetes and helm providers, we need fine-grained outputs for cluster address, client certificate, key, etc.

To test this, consider the following Terraform snippet, which can be plugged into the AWS Terraform example configuration:

provider "kubernetes" {
  host = constellation_cluster.aws_example.host

  client_certificate     = constellation_cluster.aws_example.client_certificate
  client_key             = constellation_cluster.aws_example.client_key
  cluster_ca_certificate = constellation_cluster.aws_example.cluster_ca_certificate
}

data "kubernetes_nodes" "example" {}

output "node-ids" {
  value = [for node in data.kubernetes_nodes.example.nodes : node.spec.0.provider_id]
}

Proposed change(s)

• Parse the kubeconfig returned through the init RPC and extract the respective values, making them available as outputs of the constellation_cluster resource.

Additional info

• AB#4604

Checklist

• Update docs
• Add labels (e.g., for changelog category)
• Is PR title adequate for changelog?
• Link to Milestone

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