Default error schema 422

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Added a default schema for 422 status codes, similar to FastAPI. The functionality ensures that a schema is only added if http422 is not already present in the response.

if http422 not in result:
    model = operation._create_response_model_multiple({http422: DefaultValidationError})[http422]
    schema = self._create_schema_from_model(model)[0]
    result[http422] = {
        "description": "Validation error",
        "content": {self.api.renderer.media_type: {"schema": schema}},
    }

The function operation._create_response_model_multiple({http422: DefaultValidationError})[http422] is a method within the class that generates the model. If you know of a better approach to create this model without directly invoking the class method, please suggest improvements, and I will update the implementation accordingly. 🙂

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