Deprecate the codelab in favour of the Kubeflow GKE end-to-end guide

[sarahmaddox]

We now have an end-to-end GKE guide in the Kubeflow docs, which uses the code sample from this codelab.

Here's the new Kubeflow doc: https://www.kubeflow.org/docs/guides/gke/gcp-e2e/

It'd be good to deprecate this codelab in favour of the Kubeflow docs and samples. I think the steps needed are:

1. Merge the code sample from this repo into the Kubeflow samples repo.
2. Deprecate the codelab tutorial: https://codelabs.developers.google.com/codelabs/kubeflow-introduction/index.html#0