Introduce centralized configuration object

[GernotMaier]

It is cumbersome to propagate the command line configuration throughout the code - adding a single parameter might lead to multiple hard to find changes throughout the code.

Suggest to use use a centralized configuration object with controlled mutability:

# config.py
from types import MappingProxyType

class _Config:
    def __init__(self):
        self._cfg = {}

    def load(self, args: dict):
        self._cfg = MappingProxyType(args)  # immutable view

    @property
    def data(self):
        return self._cfg

config = _Config()

and

# main.py
import argparse
from config import config

args = vars(argparse.ArgumentParser(...).parse_args())
config.load(args)

# anywhere
from config import config
print(config.data["input_file"])
``

[GernotMaier]

• paths PR Introduce flexible definitions of CORSIKA and sim_telarray paths #1921
• db_config PR Use db_config from new settings module #1927
• args_dict