WIP: Introduce generator as option for base

[justinsb]

No description provided.

[justinsb]

Marking as WIP for discussion. This is intended to address generators (example prior discussion #2528, though I think this only helps with a subset of those use-cases).

[justinsb]

This will allow e.g.

apiVersion: porch.kpt.dev/v1alpha1
kind: PackageRevision
metadata:
  namespace: default
  name: "deployment:postgres:v1"
spec:
  packageName: postgres
  revision: v1
  repository: deployment
  tasks:
  - type: clone
    clone:
      generator:
        config:
          apiVersion: fn.kpt.dev/v1alpha1
          kind: RenderHelmChart
          helmCharts:
          - chartArgs:
              name: postgresql
              repo: https://charts.bitnami.com/bitnami
            templateOptions:
              values:
                valuesInline:
                  postgresqlDataDir: /kpt/postgresql/data
  - type: eval
    eval:
      image: gcr.io/kpt-fn/set-labels:v0.1.5
      configMap:
        bucket-label: bucket-label-value
        another-label: another-label-value

[justinsb]

I uploaded a bit more in #3041 which shows how we could discover the function for a CRD