Creating Pipeline with duplicate name fails in UI with 500

[rmgogogo]

What steps did you take:

Creating Pipeline with duplicate name fails in UI with 500

What did you expect to happen:

Either allow create pipeline with same name or provide better msg.

Environment:

How did you deploy Kubeflow Pipelines (KFP)?

KFP version:

KFP SDK version:

Anything else you would like to add:

[Miscellaneous information that will assist in solving the issue.]

/kind bug

[Bobgy]

This is expected behavior, but we can improve on error message I think. (in fact every api call needs some improvement on error message)