Add -r registersfilename commandline argument

[norrland]

Allow specifying the registerfile from commandline.

ex:
$ python3 sungather.py -c /path/to/config.yaml -r /other/path/registers-sungrow.yaml

[bohdan-s]

What is the use case for this?
The idea of the registers file is it provides for every model in a single file.

[norrland]

Sorry for no context.
I have SunGather running on a FreeBSD host in python virtualenv. When running it as a service, the os.cwd() won't be in the base of the sungather directory. In the service file I set the base configuration path for both config.yaml and registers-sungrow.yaml. The -r flag allows me to call the sungather.py from wherever.

[bohdan-s]

Sounds like good functionality to add! Thank you