Integration of AirClim 2.1 contrail module

[liammegill]

The first version of oac.cont is equivalent to the contrail module of AirClim 2.1.

[liammegill]

I have been trying to figure out this relative folder structure so that the files within utils/ can be loaded in tests/ but still run independently. I came across this thread: https://stackoverflow.com/questions/16981921/relative-imports-in-python-3. I think I have solved the problem now by including the following in the header of any file that should also be able to run on its own:

SCRIPT_DIR = os.path.dirname(os.path.abspath(__file__))
sys.path.append(os.path.dirname(SCRIPT_DIR))

Unfortunately, pylint is not too happy with this because you should ideally first import everything before defining variables (https://pylint.readthedocs.io/en/latest/user_guide/messages/convention/wrong-import-position.html). But this is the only way I have managed to get this to work... I will now try committing a new version to see whether this (finally) passes the checks.

[stefan-voelk]

feature/cont looks good and GitHub Actions successfully passed through! Merging to dev can go ahead.