Make `model` optional in `CreateModelResponseQuery` when referring prompts by "prompt_id"

[Alkenso]

Is your feature request related to a problem? Please describe. Latest OpenAI API supports using prompts by ID creating prompts in Prompt Management Playground and later referring them by "prompt_id" when using with Responses API. If such case model is not required and user can only specify input.

Describe the solution you'd like Add ability to omit model in CreateModelResponseQuery initializer.