[BUG] add default response handling

[spacether]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
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• What's the actual output vs expected output?
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Description

If there is only a default response, it should be used when deserializing
If there is a 200 and a default, the default should be used when deserializing non-200 responses

openapi-json-schema-generator version

OpenAPI declaration file content or url

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

[spacether]

This is already handled per the endpoint template