Look into declarative configuration

[tobixen]

See if this boilerplate pattern can be used for the caldav library: https://setuptools.pypa.io/en/latest/userguide/declarative_config.html

credits to @mgorny in https://github.com/python-caldav/caldav/commit/3a1aea68905d12131fa412a6424bc84917509354#r96436457