Convention for API Errors

[Monstarrrr]

Blocking #219 & #220

We preferably need to return errors in one single coherent format :
We should not return error messages in a different structure for api/ (our custom routes) than it is being returned in auth/ (djoser), so we either reproduce the same structure as how djoser handles errors, or we override djoser's)

https://www.django-rest-framework.org/api-guide/exceptions/#custom-exception-handling

The drf-standardized-errors package provides an exception handler that generates the same format for all 4xx and 5xx responses. It is a drop-in replacement for the default exception handler and allows customizing the error response format without rewriting the whole exception handler. The standardized error response format is easier to document and easier to handle by API consumers.

Integration with drf-spectacular
https://drf-standardized-errors.readthedocs.io/en/latest/openapi.html