Simplify output directory name/path

[simi2525]

We have to simplify the output directory situation, we should override in some way the hydra-core file structure, ideally, our custom run name/tags should be first, and differentiation based by date/hour should be deeper in the file structure, making it easier to read from tensorboard.
As a second step, we should add a more easy-to-use parameter to override/replace/append to the custom/aux path to make it much easier to have custom names for our runs, moving "aux_save_dir" at the start of save_dir, could be the simplest way (and rename it)
So we can run things like: "python main.py tag=increased_lr_same_model" and to have this be easily readable from tensorboard.