Create hydranet main

[Polichinel]

Created a main.py for purple alien.

But more importantly, this is to be seen as a suggestion to a more general structure. I.e. both how the main is structured, the use of agr parse, and the associated common_utils. But also further the way that the hierarchic of scripts main.pt<-model_run_handlers<-model_run_managers<-(training, testing, forecasting scripts respectively) ids set up.

We should think about how much of this we can abstract out to common_utils. Of course, the deeper we go into these hierarchies the less we should expect the code to be generalizable.

Thanks in advance for any notes and feedback!

[Polichinel]

Comments to Sara's comments.

Generally followed advice. changed os the pathlib throughout the script, renamed some script and relocated to central scripts to new dir src/management as they seemed too important to hide in utils, but we still want a clean main.py. LMKWYT.

Add some new functions to set_path script to accommodate ESCW PR, but with a change so the PATH_MODEL has its own function (setup_model_path) and is not part of the setup_data_paths