The additional_config functionality works, but this is already a feature of Hydra (Docs). Adding ../additional_config to train.yaml as a Hydra searchpath achieves the same functionality, without cluttering the code with an unneeded plugin.
When hardcoding the location of additional_config, it might be good to add both an __init__.py and a .gitkeep.

I didn't get it to work the way I wanted (in the order that it will be overwritten). Did you manage to keep the functionality as mentioned? I think the plugin might still be interesting, as we can also extend it to read directly from repositories.

It seems that this plugin would still be interesting with the possibility to extend it to read directly from repositories.

I have two comments regarding the expected behaviour of this PR:

1. In manipulate_search_path no warning is given if the additional_path is not a directory. Perhaps logging something something simple, such as "Only using standard ahcore config folder for Hydra configurations.", would be good to avoid any confusion.
2. The env.load_env function starts searching recursively from ahcore/utils folder instead of the working directory. It will find the .env folder if it is in a parent folder but not when placed in the tools directory.

@BPdeRooij I believe I have addressed both concerns.

dotenv.load_dotenv expects an explicit file name. It does not start searching from working_dir. For this we could use dotenv.find_dotenv(usecwd=True) and give this as dotenv_path