How to manage a lot of actions in actions.py

Not quite: say you have an actions directory as follows:

actions/__init__.py
       /some_common_code.py
       /actions1.py
       /actions2.py
       /actions3.py

You can organise your actions as a regular python package: perhaps some modules import other, etc
As far as I’m aware, the server will load all your code this way, but will register actions by looking at your classes definitions (ActionAbc(Action)will get registered, but SomeOtherClass(object) won’t).

For Dockerfile, yes, as @simonm3 wrote, you need to copy the whole actions folder