Directly load configuration values from environment variables instead of relying on Django settings

[stevenbal]

In Open Inwoner we are implementing setup_configuration and we were wondering if it is really necessary for every configuration variable to be defined as a setting.

From my understanding it was originally implemented using settings, because there could be certain settings that have defaults (which should also be used when running setup_configuration), but in the case of Open Inwoner we have several steps that don't use any defaults, leading to a lot of duplication because we have to define settings for everything: https://github.com/maykinmedia/open-inwoner/blob/develop/src/open_inwoner/conf/app/setup_configuration.py#L17

@annashamray is directly loading variables from the environment maybe something that could be possible next to using settings?

[annashamray]

Sergei also proposed to remove settings layer cause it's unnecessary.
Having them both could be a solution. We can first check the setting and if it doesn't exist we can check the environment.
I don't mind this approach.

[alextreme]

@sjoerdie I think this issue is what you mentioned would be preferable, right?