How to make OpenAIGenerator generate JSON format

[dinhquangson]

Hi there,

In haystack, i used
generator = OpenAIGenerator(
api_key=Secret.from_env_var("OCTOAI_TOKEN"),
api_base_url="https://text.octoai.run/v1",
model="mixtral-8x22b-instruct",
generation_kwargs = {"max_tokens": 512}
)
It makes JSON format, but it appends some text behind. How to work arround it