feat(runtimes): add Pending and Running status conditions for TrainJob

[RohitYandigeri]

Fixes #2713

This PR improves TrainJob observability by adding intermediate status
conditions that reflect the lifecycle of the underlying jobs.

What’s added

• Pending condition when a TrainJob is created but underlying jobs have not started
• Running condition when underlying jobs are actively executing
• Status is derived from Job-level signals via the TrainJobStatus framework plugin
• kubectl get trainjob now reflects these states consistently

Notes

• Status is not set during TrainJob creation (controller-owned status), in line
  with Kubernetes conventions
• CRD regeneration could not be performed locally on Windows; happy to update
  manifests if requested

Why

This aligns TrainJob with standard Kubernetes resource status patterns and
provides better UX for users monitoring training lifecycle.

cc @kubeflow/kubeflow-trainer-team

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[github-actions]

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[andreyvelich]

Thank you for this contribution @RohitYandigeri!
As we discussed before, Job Active condition doesn't indicate that training process is running. Sometime, PyTorch can stuck in initialization phase or synchronization phase. Kubernetes Batch/Job doesn't detect that.

As part of this KEP: #2905, we are working on exposing training progress to the TrainJob status. That will help us to detect that the actual model training process is happening.

cc @robert-bell @kubeflow/kubeflow-trainer-team

Let's hold this PR for now, and discuss more details in 2905
/hold