[ENHANCEMENT] Add southbound traffic support for CNP API

Superceeds https://github.com/kubernetes-sigs/network-policy-api/issues/127 and https://github.com/kubernetes-sigs/network-policy-api/pull/128 and https://github.com/kubernetes-sigs/network-policy-api/pull/249 which were tracking use cases/user stories for this.

**Is your enhancement request related to a problem? Please describe.**
`Nodes` and `Networks` are only supported as Egress Peers.

**Describe the solution you'd like**
`Nodes` and `Networks` should also be supported as Ingress Peers.

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**
Add any other context or screenshots about the feature request here.