Allow Jupyter pod to scale workers

[jacobtomlinson]

Currently the Jupyter Notebook instance which is deployed as part of the helm chart can connect to the Dask cluster in order to use it, but it has no permissions on the Kubernetes cluster it is deployed on.

In dask/dask-kubernetes#255 we are adding a HelmCluster cluster manager which allows users to access logs and scale the workers deployed via the Helm Chart.

In order to use the cluster manager, you must have permissions to modify Deployment resources and access Pod log resources. It is assumed that those able to install the helm chart will have those permissions.

However if you deploy the helm chart and then make use of the provided Jupyter session then your credentials will not be available without some manual copying. Therefore the HelmCluster manager requires some additional configuration steps before it can work.

It could be helpful to include an optional service account in the helm chart which is made available to the Jupyter pod which has permission to scale the deployment and access logs.

cc @gforsyth @raybellwaves

[jacobtomlinson]

When resolved this warning in dask-kubernetes should be updated.