Draft: scripts/k8s-access: setup multiple clusters at once

This has different advantages:

• because there is only one task it's more easy to depend on it

  eg:

  pre_tasks: foo: exec.#Run & {
    $after: pre_tasks.k8s_access
    cmd: ["kubectl", "..."]
    env: KUBECONFIG: pre_tasks.k8s_access.stdout
  }

  This design would allow to build higher level definitions for kubectl, eg:

  #KubectlApply: {
    data: {
        apiVersion: string
        kind: string
        ...
    }
  
    exec.#Run
    $after: pre_tasks.k8s_access
    cmd: ["kubectl", "apply", "-f", "-"]
    stdin: json.Marshal(data)
    env: KUBECONFIG: pre_tasks.k8s_access.stdout
  }

• no lock handling

• less tasks to generate