Creates a completion for the chat message
role (string): system, user, or assistantcontent (string | array): The message contentchat.completion.index (integer): Index of the choicemessage (object): The generated messagefinish_reason (string): Why the model stopped (stop, length, tool_calls)prompt_tokens (integer): Tokens in the promptcompletion_tokens (integer): Tokens in the completiontotal_tokens (integer): Total tokens used