Add cmd for importing Kubernetes API schemas

[stefanprodan]

ℹ️ This command was renamed to timoni mod vendor k8s in #197

This PR adds a new command for simplifying the import and generation of CUE schemas for Kubernetes APIs.

The timoni mod import k8s along with timoni mod import crd improve the UX of developing and maintaining app modules.

Motivation

Currently module authors have to install Go, create a dummy Go module, run go get for all the Kubernetes API Go packages for a specific Kubernetes version, then run cue get go for each API group to generate CUE schemas out of the Go types. Keeping this schemas up to date with the Kubernetes releases is a tedious process, since the Go types depend on each other e.g. k8s.io/api/apps/v1@0.28.2 depends on k8s.io/api/core/v1 which depends various packages under k8s.io/apimachinery.

Solution

Timoni offers a simple command for importing and updating all the Kubernetes builtin APIs for a specific minor version.

$ timoni mod import k8s -h
Import Kubernetes API CUE schemas

Usage:
  timoni mod import k8s [MODULE PATH] [flags]

Examples:
  # Import the latest Kubernetes API schemas
  timoni mod import k8s

  # Import s specific minor version of the Kubernetes API schemas
  timoni mod import k8s -v 1.28

The timoni mod import k8s command pulls the CUE schemas from GitHub Container Registry. These schemas are generated after each Kubernetes minor release in the kubernetes-cue-schema repository and published as OCI artifacts at ghcr.io/stefanprodan/timoni/kubernetes-schema.

For each Kubernetes minor version, a dedicated set of CUE schemas are generated for the following Kubernetes GA APIs:

• k8s.io/api/admission/v1
• k8s.io/api/admissionregistration/v1
• k8s.io/api/apps/v1
• k8s.io/api/authentication/v1
• k8s.io/api/authorization/v1
• k8s.io/api/autoscaling/v2
• k8s.io/api/autoscaling/v1
• k8s.io/api/batch/v1
• k8s.io/api/certificates/v1
• k8s.io/api/coordination/v1
• k8s.io/api/core/v1
• k8s.io/api/discovery/v1
• k8s.io/api/events/v1
• k8s.io/api/networking/v1
• k8s.io/api/node/v1
• k8s.io/api/policy/v1
• k8s.io/api/rbac/v1
• k8s.io/api/scheduling/v1
• k8s.io/api/storage/v1