Is there an existing issue for this?

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Is your feature request related to a problem? Please describe the problem.

There are some cases where the framework / middleware pipeline can generate error responses, such as when the endpoint defines a required parameter -- if the parameter is not present in the request, the framework generates a status code 400 response. And if the ProblemDetails service was added to the DI container, it is used to generate a ProblemDetails response body for this.

However, these responses are not represented in the generated OpenAPI document.

Describe the solution you'd like

For the case indicated, and perhaps others, these responses should be included in the generated OpenAPI document. However, I think we'll want to be careful about this -- for example I'm not sure we should add 401 and 403 responses for operations that require authentication.

Additional context

No response