[Feature] Add docstrings for our metric objects

### Feature Request ```python class Metric(BaseModel): name: str metric_type: Literal["Metric"] = "Metric" identifier: str = "" model_config = ConfigDict(frozen=True) description: str | None = None ``` We need to add docstrings (ideally using the Field param) here so they show up when people try to make them. ### Additional Context _No response_