Provide notebook pip requirements and default kubeflow version in example env

[ukclivecox]

This change is 

[jinchihe]

/lgtm

[jinchihe]

/approve

[jinchihe]

Oh...Sorry, seems I have not fully approve permission.

/approve cancel

[ryandawsonuk]

/lgtm
/approve

[k8s-ci-robot]

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[ryandawsonuk]

/assign @jinchihe

[jinchihe]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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