return tool calls finish reason for openai (#5995)

* hot fix

* backend stream support

* clean up

* finish reason

* move to openai

openai/openai.go

@@ -218,6 +218,9 @@ func toChatCompletion(id string, r api.ChatResponse) ChatCompletion {
 			Index:   0,
 			Message: Message{Role: r.Message.Role, Content: r.Message.Content, ToolCalls: toolCalls},
 			FinishReason: func(reason string) *string {
+				if len(toolCalls) > 0 {
+					reason = "tool_calls"
+				}
 				if len(reason) > 0 {
 					return &reason
 				}