How to add oneOf to the schema

type Response struct {
	field1   *string           `json:"field1,omitempty"`
	field2   *string          `json:"field2,omitempty"`
}

I want to indicate that the response will either contain field1 or field2

Sample spec:
```
    Response:
      oneOf:
        - $ref: '#/components/schemas/Response1'
        - $ref: '#/components/schemas/Response2'
```