Implement missing HTTP status code pages #442
Description
The folder src/Controller/Error/assets contains text files for all problematic status codes returned by the API, however at least one status code is missing: 405.
Acceptance criteria:
- Check whether there are other missing status code files.
- Implement missing status code files.
- Add missing documentation pages.
- Add tests to make sure these problem status code files can not get removed by accident in the future.