Clean up metric columns

[jingzhang36]

Internal bug thread b/135048320, reporting the metric columns of some runs are missing when displayed in RunList. This is not actually a bug but because the runs of the list are not required to have the same set of metrics and we currently show metric columns based on the first run in the list.

Reasoning:

1. Given the fact that the main intention of displaying metric columns in a run list is for comparing these metrics across runs, we can conclude that the metric columns in run list make sense if the runs under comparison have the same set of metrics. On the other hand, in AllRun list, the runs are from all runs of unrelated pipelines in the system, and their metric sets have no inherent connection or comparison need. Therefore, in the AllRun list, we disable metric columns display.

2. Meanwhile, e.g., if our users want to compare metric columns of runs from a same pipeline and hence having same metric columns, it is still available. They can leverage our "Experiment" feature. I.e., if they group runs of same metrics to a single experiment, our run list of a same experiment has the metric columns displayed.

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This change is 

[jingzhang36]

/assign @Bobgy

[Bobgy]

Thanks! That sounds reasonable to me.
/lgtm
/approve

Do you need to ask anyone else's opinion? If not, please unhold

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Bobgy

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[jingzhang36]

@Bobgy Thanks for the review and update: In b/135048320, Katie lgtm'ed. So
/unhold

[k8s-ci-robot]

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Test name	Commit	Details	Rerun command
kubeflow-pipeline-e2e-test	7073dd9	link	/test kubeflow-pipeline-e2e-test

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