Dynamically validate error responses too

[tazlin]

As of Haidra-Org/AI-Horde@5c5d3dd, there should be enough information in the swagger to dynamically valid error responses. write_all_response_examples_to_file in swagger.py already has a bool keyword argument error_responses which will write out all of the published error responses to json for pytest/CI.

Some thoughts:

• The API is missing some possible HTTP return codes for errors (this is often because nested function calls can make it difficult to determine which exceptions might be raised and changes to shared functions make it hard to identify which endpoints to decorate with the possible new return codes).
• As of today, all of the example errors are identical. It may or may not serve us to include examples which vary from endpoint to endpoint (or at least, vary at all).