Add support for custom JSON payload in ChatCompletionContentPart

[FanYaning]

Fix: #700

        ChatCompletionContentPart textPart = ChatCompletionContentPart.ofText(ChatCompletionContentPartText.builder()
                .text(promptMessage)
                .build());

        String type = visionMessage.startsWith("data:image/") ? "image_url" : "video_url";
        Map<String, JsonValue> part = Map.of(
                "type", JsonValue.from(type),
                type, JsonValue.from(Map.of("url", visionMessage)));

        ChatCompletionContentPart visionPart = ChatCompletionContentPart.ofJson(JsonValue.from(part));

        ChatCompletionCreateParams createParams = ChatCompletionCreateParams.builder()
                .addUserMessageOfArrayOfContentParts(List.of(visionPart, textPart))
                .model(config.getModelV())
                .temperature(config.getTemperatureV())
                .putAllAdditionalBodyProperties(customProps)
                .build();

[Guokeeng]

我也遇到这个问题了，很需要这个提交，怎么4个月了都没人复审呢？？？