[BUG] OepnAI JSON format

[tinyrolls]

Describe the bug
The JSON response format's input structure for OpenAI's API appears to have changed to { "type": "json_object" }, causing compatibility issues with existing implementations.

To Reproduce
Code to reproduce

pipeline.run(
    parameters={
        "task_with_openai": {
            "llm": {
                "generation_kwargs": {
                    "response_format": "json"
                }
            }
        }
    }
)

Expected behaviour
openai.BadRequestError: Error code: 400 - {'error': {'message': "Invalid type for 'response_format': expected an object, but got a string instead.", 'type': 'invalid_request_error', 'param': 'response_format', 'code': 'invalid_type'}}

**Additional context
it should be kwargs["response_format"] = {"type": response_format}

distilabel/src/distilabel/llms/openai.py

Line 304 in 844165f

kwargs["response_format"] = response_format

[plaguss]

Hi @tinyrolls, thanks for noticing, this PR should fix it: #1053