Jupyter single user add more restrictive network access policies

investigate and add network policies to block singleuser from accessing internal ip addressesses/pods

see for reference: https://zero-to-jupyterhub.readthedocs.io/en/latest/administrator/security.html#kubernetes-network-policies

Start by locating the Jupyter single-user and Kubernetes network-policy configuration in the repository, then read the linked Zero to JupyterHub security reference. Define the policy so single-user environments cannot reach internal IP addresses or pods, while documenting and testing the intended allowed access.

Written by the indexing model from the issue text.