Make raise_on_unexpected_status a generation option

[linde12]

I'm using client combined with raise_on_unexpected_status so i would like the API functions (sync & asyncio) to return T instead of Optional[T]

I know raise_on_unexpected_status is a runtime flag right now, but to me it makes more sense to have it as a build/generation time flag. The workaround is disabling linting or using cast everywhere, but it quickly gets tedious and very ugly.

See https://github.com/openapi-generators/openapi-python-client/blob/main/openapi_python_client/templates/endpoint_module.py.jinja#L71