Change the type of resource reference payload column (#1905)
Change the type of resource reference payload column (#1905)

Gorm doesn't automatically change the type of a column. This changes introduced a column type change which might not be effective for an existing cluster doing upgrade. 
https://github.com/kubeflow/pipelines/commit/4e43750c9dcebe37b75aedadd7b1c829b409caaa#diff-c4afa92d7e54eecff0a482cf57490aa8R40

/assign @hongye-sun
kubeflow/pipelines,kubeflow/pipelines,kubeflow/pipelines,kubeflow/pipelines,kubeflow/pipelines,kubeflow/pipelines