non-zero exit code when part of api fails to generate

[willr3]

We have an openapi.yaml that we want to use to generate a python client as part of our automation. Our openapi.yaml has some text/plain under responseBody.content.
I know that is currently not supported but it would be nice if our automation scripts could detect the issue by checking the exit code instead of having to parse the output for WARNING.

[willr3]

I see fail_on_warnings in cli.py. When I get back to my computer in about a week I will try and set that option