Using `previous_pipeline_directory` should return an absolute path instead of a relative one if possible.

[eddiebergman]

If running a pipeline like below, then NePs will nicely inject the previous_pipeline_directory:

def run_pipeline(previous_pipeline_directory: Path, **config) -> dict:
    ...

However this path is relative, essentially I get the following path, neps_root_directory/results/config_2_0, it could make things a bit smoother to have this as an absolute path, i.e. for logging or any more complex post analysis behaviours.

[eddiebergman]

As a side note, it would also be nice to have access to the current config_id within run_pipeline, however it can be easily calculated.