Add document on Stackdriver agents

[lluunn]

We should add document to GKE get started guide about the new Stackdriver agents. They should be deployed with DM, and what are the features, how to use them.

[sarahmaddox]

This issue was moved to kubeflow/website#211

[sarahmaddox]

/close

[k8s-ci-robot]

@sarahmaddox: Closing this issue.

In response to this:

/close

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