Add visual output to KubeCluster while it is starting up

Currently when you create a `KubeCluster` object it silently hangs until the scheduler has been created.

I typically also have `kubectl`/`k9s` in a separate terminal so I can watch what is going on. But really we should feed back to the user through the Python API.

In `dask-cloudprovider` we make heavy use of `cluster.log()` to emit information to the user. At the very least we should do the same for `KubeCluster`.

We could also take this further and use [`rich`](https://rich.readthedocs.io/en/latest/introduction.html) to provide some more visual output of the state of the cluster with status indicators that update rather than print line by line. Coiled does this with their cluster manager.

While a cluster is starting we typically want to know what the controller is doing (which we can communicate through custom resource statuses) and what the status of the individual Pods are.