Add past_feat_dynamic_real to MetaData

[jmberutich]

Would be great if we can also include past_feat_dynamic_real to the dataset MetaData, so it can be used downstream in TFT.

Change should be quite simple by simply adding one line to the dataset MetaData class in common.py:

class MetaData(pydantic.BaseModel):
    freq: str = pydantic.Field(..., alias="time_granularity")  # type: ignore
    target: Optional[BasicFeatureInfo] = None

    feat_static_cat: List[CategoricalFeatureInfo] = []
    feat_static_real: List[BasicFeatureInfo] = []
    feat_dynamic_real: List[BasicFeatureInfo] = []
    past_feat_dynamic_real: List[BasicFeatureInfo] = []
    feat_dynamic_cat: List[CategoricalFeatureInfo] = []

    prediction_length: Optional[int] = None

[ayushthe1]

Hey @jmberutich ,I would like to work on this issue .please assign it to me.