Use kuberentes condition types rather than the custom kpt "condition" type

[liamfallon]

kpt uses its own custom condition type rather than the standard k8s condition type

The standard condition type has two extra fields LastTransitionTime and ObservedGeneration, which will appear with default values for now. Over time, these fields can be properly populated.

The main reason to change is that

• the two new fields are helpful
• there are multiple unnecessary translations between the custom kpt condition type and the default type int he code, which are unnecessary.

[aravindtga]

Analysis Details:

kpt's Kptfile uses a custom Condition type that is a simplified version of metav1.Condition (missing LastTransitionTime and ObservedGeneration). Ideally we'd use metav1.Condition directly to align with Kubernetes conventions and leverage the standard helper library (meta.SetStatusCondition, meta.IsStatusConditionTrue, etc.).

However, kpt serializes Kptfiles using sigs.k8s.io/kustomize/kyaml which is a fork of gopkg.in/yaml.v3. This library only respects yaml struct tags.

metav1.Condition is defined as:

  type Condition struct {
      Type               string          `json:"type" protobuf:"bytes,1,opt,name=type"`
      Status             ConditionStatus `json:"status" protobuf:"bytes,2,opt,name=status"`
      ObservedGeneration int64           `json:"observedGeneration,omitempty" protobuf:"varint,3,opt,name=observedGeneration"`
      LastTransitionTime Time            `json:"lastTransitionTime" protobuf:"bytes,4,opt,name=lastTransitionTime"`
      Reason             string          `json:"reason" protobuf:"bytes,5,opt,name=reason"`
      Message            string          `json:"message" protobuf:"bytes,6,opt,name=message"`
  }

Two problems:

1. No yaml struct tags. kyaml falls back to lowercased field names (lasttransitiontime instead of lastTransitionTime, observedgeneration instead of observedGeneration)
2. No omitempty on required fields - LastTransitionTime, Reason, and Message are required in the k8s API so they lack omitempty. This causes zero values to always serialize (lasttransitiontime: "0001-01-01T00:00:00Z", message: ""), polluting the Kptfile output.

Result when using metav1.Condition directly with kyaml:

  # Expected
  - type: Rendered
    status: "True"
    reason: RenderSuccess

  # Actual
  - type: Rendered
    status: "True"
    observedgeneration: 0
    lasttransitiontime: "0001-01-01T00:00:00Z"
    reason: RenderSuccess
    message: ""

Switching to sigs.k8s.io/yaml (which respects json tags) is not feasible because kyaml provides comment preservation, field ordering, and sequence indentation control that kpt depends on.

PR with the change required for metav1.Condition: #4548

Is there a better path to use metav1.Condition natively, or should we accept the custom struct with conversion helpers as the long-term approach?