Add a generate command

This is the second part of the side that is more relevant for the datahub (@cwerner). With this PR I am adding an initial draft of a generate command that generates the frontend API module

At the moment this does only generate the API. But I aim to create the entire module automatically using the datamodel-code-generator.

Usage example:

python ExampleMessageConsumer.py -t test generate

produces the following

python code:

"""
Example backend module for the de-messaging framework.

Start this module by typing::

    python ExampleMessageConsumer.py -t your-custom-topic connect

in the terminal, or::

    python ExampleMessageConsumer.py --help

for further options.
"""
from __future__ import annotations


def hello_world(message: str, repeat: int, greet_message: str) -> __main__.GreetResponse:
    """
    Greet the hello world module.

    Parameters
    ----------
    message: str
        Message that will be part of the greet response
    repeat: int
        Number of repetitions of the greet message
    greet_message: str
        Message string that will be mirror back to the requesting node

    Returns
    -------
    GreetResponse
        Hello world greet response object
    """
    pass


class HelloWorld:
    """
    Greet the world from a class.

    Classes can define the methods that shall be used for the backend, and they
    define a constructor. 
    """

    def __init__(self, message: str):
        """
        Parameters
        ----------
        message: str
            The hello message
        """
        pass

    def repeat_message(self, repeat: int) -> List[str]:
        """
        Repeat the `message` multiple times.

        Parameters
        ----------
        repeat: int
            The number of times, `message` shall be repeated.
        """
        pass