Add CompletionRequest.StreamOptions (#959)

The legacy completion API supports a `stream_options` object when
`stream` is set to true [0]. This adds a StreamOptions property to the
CompletionRequest struct to support this setting.

[0] https://platform.openai.com/docs/api-reference/completions/create#completions-create-stream_options

Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

completion.go

@@ -215,6 +215,8 @@ type CompletionRequest struct {
 	Temperature     float32           `json:"temperature,omitempty"`
 	TopP            float32           `json:"top_p,omitempty"`
 	User            string            `json:"user,omitempty"`
+	// Options for streaming response. Only set this when you set stream: true.
+	StreamOptions *StreamOptions `json:"stream_options,omitempty"`
 }
 
 // CompletionChoice represents one of possible completions.