Add Liquigraph support

This is a long-standing issue. I tried that several times but did not get it to work (dunno why) but yesterday had an epiphany and it worked on the first try. This will allow us to do migrations for Neo4j data. We previously did that manually by collecting them in the issue. I think this will provide us with a lot more flexibility.

The downside is that it will not work in tests because of the use of the embedded Neo4j database. We also have other issues because of that, see #85 (closed) as example. I think it might make sense to investigate the use of TestContainers and use that instead.

The configuration in the MR is not used yet. It just sets it up for use.