Include network policy documentation on website

## Feature Request

Current documentation around network policies and linkerd is quite sparse. The only document is on medium.

https://medium.com/@ihcsim/linkerd-2-x-with-network-policy-2657103333ca#:~:text=A%20network%20policy%20defines%20ingress,communication%20within%20a%20Kubernetes%20cluster.

### What problem are you trying to solve?

Have up to date network policy documentation

### How should the problem be solved?

Migrate and update medium article and include it on the website

What do you want to happen? Add any considered drawbacks.

See above

### Any alternatives you've considered?

No

Is there another way to solve this problem that isn't as good a solution?

Not sure

### How would users interact with this feature?

If you can, explain how users will be able to use this. Maybe some sample CLI
output?

Start by reviewing the linked Medium article and the website repository's existing documentation structure. Migrate and update the network policy content for Linkerd and Kubernetes, then confirm that the documentation is included on the website and is current.

Written by the indexing model from the issue text.