Validate responses from exception handlers

[matez0]

Hi,
In the OpenAPI specification of the request handlers, it is possible to declare response schemas for different response status, but if the response is generated by an exception handler, it will not be validated like normal responses.
This can lead to inconsistent OpenAPI specification and implementation.

What about wrapping the on_exception calls in the Operation class (e.g.

django-ninja/ninja/operation.py

Line 127 in eecb05f

return self.api.on_exception(request, e)

) with validation of the return value?

If it is a good idea, I can make a PR for it.

This proposal would be a solution for this question:
#1118 (comment)