Use config file instead (or additional to) of CLI parameters

[jbeyerstedt]

When starting this script automatically, e.g. with systemd, it’s better to separate the configuration from the startup script.

So add a parameter where to find a config file, make the currently mandatory parameters optional and just use the CLI parameters as an overwrite for the config file. Also add the parameters, which are configured in the python script itself (sysID, ICAO code, etc.) to the config file.