feat(v2): enable v2 compatible mode in full Kubeflow with zero config. Fixes #5680

[Bobgy]

Description of your changes:
Fixes #5680
Investigation and rationale are logged in #5680.

Changes:

• Makes default pipeline root configurable via key defaultPipelineRoot in a configmap named kfp-launcher in the same namespace as the pipeline run.
• Defaults minio service to the same namespace via MINIO_SERVICE_SERVICE_HOST env var. When not found, fallbacks to minio-service.kubeflow:9000 (default service name of MinIO in full Kubeflow).

How this PR makes kfp v2 compatible run on Kubeflow:

1. For distributions using MinIO, now we can auto discover the minio service in kubeflow namespace.
2. For distributions not using MinIO, they can configure default pipeline root to other storage URL, e.g. for Kubeflow on GCP, we can default pipeline root to a GCS path during deployment via key defaultPipelineRoot in a configmap named kfp-launcher in the same namespace as the pipeline run

As a follow up, #5750 makes defaultPipelineRoot configurable as defaultPipelineRoot field in pipeline-install-config for both KFP standalone and multi-user mode.

Checklist:

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[Bobgy]

/assign @capri-xiyue

[Bobgy]

/hold
I haven't successfully verified in full Kubeflow deployment

EDIT: this doesn't work on kubeflow on GCP, see #5680 (comment)

[Bobgy]

/unhold
The default values should work for most Kubeflow distributions that have a centralized MinIO service with bucket mlpipeline. So this seems enough. See #5680 (comment).

For making default pipeline root work in other distributions, we need a way to configure default pipeline root.

[capri-xiyue]

Is it possible that user defines a configmap but doesn't define the "defaultPipelineRoot" in configmap? Should we throw a error here?

[Bobgy]

I'd suggest we treat all configuration with maximum tolerance, e.g.:

• everything should have a default value
• everything is optional

Therefore, I don't throw an error here.

I did add a glog.Infof afterwards to make it obvious what we defaults to in the end. (our logging doesn't show info logs by default, but we can fix that separately)

What do you think about these choices?

[capri-xiyue]

sgtm

[capri-xiyue]

/lgtm

[Bobgy]

/approve

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