Add a proper Mailing List page

### What should happen

Only linking to the mailing list archives is not acceptable. Every ASF project website needs a page or section that describes the mailing lists and how to subscribe or unsubscribe.

Simply sending people to the archives will not bring people into the community discussions.

### Why

Follow the Apache Way

### Which layer

Other / unsure

### Boundary conditions (optional)

_No response_

### Out of scope (optional)

_No response_

### References (optional)

https://whimsy.apache.org/site/project/magpie is not a complete check as it misses the Mailing List and Download page requirements.

Start by inspecting the project website structure and the existing mailing-list archive link. Done means adding a page or section that describes the mailing lists and explains how to subscribe and unsubscribe.

Written by the indexing model from the issue text.