Investigate if the CI build can be sped up by using nixery docker images
Currently, we use an OCaml base Docker image and then execute several apt commands in order to update & install several dependencies.
This is necessary for every job of the pipeline.
As I understood Nixery creates custom ad-hoc docker images using nix machinery where the available packages can be specified in the name. Given that Docker images are cached, this could eliminate the need for the apt steps.