[feature request] Support ordered container start using initContainers

Is your feature request related to a problem? Please describe. Currently score-k8s doesn't support the before property for ordered container start (spec#104). In score-compose we already have this (score-compose#454), but score-k8s needs a different approach since Kubernetes has native initContainers.

Describe the solution you'd like Map the before property to Kubernetes initContainers:

• ready: complete - regular initContainers entry (runs to completion before main containers start)
• ready: started - native sidecar initContainers with restartPolicy: Always (starts before main containers, keeps running)
• ready: healthy - return a validation error, same as score-compose K8s initContainers don't support health-based gating natively

For example, given:

containers:
  migrate:
    image: my-app:latest
    command: ["migrate"]
    before:
      app:
        ready: complete
  app:
    image: my-app:latest

The generated manifest would place migrate in spec.initContainers and app in spec.containers.

Changes would mainly go in internal/convert/workloads.go checking each container's Before field and splitting them into initContainers vs regular containers accordingly.

Describe alternatives you've considered Could also use Kubernetes lifecycle hooks or a custom controller, but initContainers is the most natural fit and is widely supported.

Additional context

• Spec issue: score-spec/spec#104
• score-compose implementation: score-spec/score-compose#454
• The before type definitions already exist in score-go v1.14.0+
• Native sidecar support (restartPolicy: Always on initContainers) is stable since K8s v1.33

Let me know if this approach makes sense or if there's anything I should adjust.