notebooks: Add docs for notebook idleness and culling

[kimwnasptd]

We've reworked the idleness and culling behavior of the Notebook Controller in KF 1.5 https://github.com/kubeflow/kubeflow/blob/master/components/proposals/20220121-jupyter-notebook-idleness.md.

We'll need to also update our docs to inform users about:

1. How to start/stop notebooks
2. How the controller sets idleness in notebook CRs
3. Instructions to enable this, as well as migration instructions
4. Best practices for culling and start/stopping notebooks

cc @kubeflow/wg-notebooks-leads
/assign @kimwnasptd @athamark

[google-oss-prow]

@kimwnasptd: GitHub didn't allow me to assign the following users: athamark.

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In response to this:

We've reworked the idleness and culling behavior of the Notebook Controller in KF 1.5 https://github.com/kubeflow/kubeflow/blob/master/components/proposals/20220121-jupyter-notebook-idleness.md.

We'll need to also update our docs to inform users about:

1. How to start/stop notebooks
2. How the controller sets idleness in notebook CRs
3. Instructions to enable this, as well as migration instructions
4. Best practices for culling and start/stopping notebooks

cc @kubeflow/wg-notebooks-leads
/assign @kimwnasptd @athamark

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[shannonbradshaw]

@kimwnasptd any updates on this issue?