UI: Allow custom `links` to be relative

[cardoe]

Would this be possible (so that domain does not need to be configured in each link)?

customLinks:
  - url: /workflows?label=my.custom.label%foo
    name: My Custom Label

@jessesuen For the custom links, we extended the existing links feature: (https://argoproj.github.io/argo-workflows/links/) by adding another scope workflow-list, and for now links feature doesn't support that, but I think it should be possible to implement it.

Originally posted by @jiachengxu in https://github.com/argoproj/argo-workflows/issues/10447#issuecomment-1478854972