[Go] Change primitive file type to os.File and prevent unknown response type error

Created by: DouglasDwyer

This PR addresses issue #11965, which causes an unknown response type error to occur during file download, by switching the primitive data type of files in Go from *os.File to os.File. Because the client API template checks for a **os.File type when attempting to decode an HTTP response, and the target file response type is ***os.File, the correct response type is not found and an error is returned. By switching to using os.File, double pointers are eliminated and file download works.

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