[Documentation] Modify Trial templates label

/area docs

After this PR: https://github.com/kubeflow/katib/pull/1611 we should modify the Katib Trial templates label to `katib.kubeflow.org/component: trial-templates` in the [Kubeflow guides](https://www.kubeflow.org/docs/components/katib/trial-template/#configure-trial-template-specification).
