Add log probabilities for chat completion output tokens

**Describe the solution you'd like**
Add logprobs and toplogprobs in chat completion requests

**Additional context**
From the [chat completion API docs](https://platform.openai.com/docs/api-reference/chat/create):
<img width="649" alt="Screenshot 2023-12-24 at 16 40 44" src="https://github.com/sashabaranov/go-openai/assets/32068609/04a769b4-53c3-4935-98c1-b1374dcf3341">
