[FT] Pass reasoning effort to `litellm` endpoint.

## Issue encountered
There is currently no way to pass the `reasoning_effort` parameter to `litellm.completion(...)`. Without being able to turn on reasoning there is no way to do most flagship models justice. This might be a more general issue with other entrypoints too, am not familiar. LiteLLM supports optional literal values `minimal`, `low`, `medium`, `high`.

## Solution/Feature
Would like to be able to specify something like

```python
model_config = LiteLLMModelConfig(
model_name=model_name,
api_key=api_key,
generation_parameters=GenerationParameters(
reasoning_effort="high"
)
)
```

## Possible alternatives
Perhaps adding it through `GenerationParameters` doesn't make sense, in which case it could be added to `LiteLLMModelConfig` directly.