Update the suggested images in `dss create-notebook --help` to use rocks

### Why it needs to get done

The initial `dss create-notebook --help` text uses Kubeflow's upstream notebook servers as suggested images. Once we have our own rocks, we should update this help text to link our rocks.

### What needs to get done

1. Update main.py with rock image links once available

### When is the task considered done

1. when the help text uses canonical-published rocks