chore: move the docker-compose volume

[vpavlin]

I was playing around with Codex and noticed the datadir is created in root (i.e. /) of my disk, which is not great.

This PR moves the datadir to docker/ folder when you run something like

docker-compose -f docker/docker-compose.yaml up

I am also adding :z which is useful when you use SELinux to properly label the volume (https://prefetch.net/blog/2017/09/30/using-docker-volumes-on-selinux-enabled-servers/)

[dryajov]

@benbierens looks like a good change and I'd like to merge it, unless this will mess your setup?

[benbierens]

Nope, the docker-compose is just there as an example. None of the tests hinge on it.
Todo-Follow-up: volumes for the k8s setup.