New Pipeline Configurations

This MR gathers commits that create new pipeline configurations, mainly for the GNN. It also reorganises the YAML files into folders, as the list of pipeline configurations was getting too large.

Note that for the pipeline configurations dedicated for GNN trainings, the embedding section is to be ignored. This is because I've been reusing the same embeddings for all these trainings. It is therefore very clear that we really need to refactor the pipeline configurations to kind make various GNN trainings depend on a single embedding training. That is what I'll focus on after the series of MRs I'm opening are merged.