Generate realistic layout tree YAML files

Summary

In order to test the database in a somewhat realistic setup, we'll need a set of YAML files with the correct number of nodes. They should be loadable using the code in !53 (merged) (see the documentation from that MR for info about the format) and usable for test databases.

What is the expected correct behavior?

A set of YAML files is provided, either in the repo or (if too large) in a public location.

If writing YAML files proves to be hard (I have no idea if that will be the case since I wrote the code myself), documentation should be added to help newcomers with the process.