Add feature transformation support to FeatureView

franciscojavierarceo

Is your feature request related to a problem? Please describe.
FeatureViews should support transformations as well.

Describe the solution you'd like

@batch_feature_view(
    sources=[credit_data_batch],
    entities=[user],
    mode="python",
    batch_schedule=timedelta(days=1),
    schema=[Field("user_id", String), Field("timestamp", Timestamp), Field("current_balance", Float64)],
)
def user_last_balance(transactions):
    return transactions[["user_id", "timestamp", "current_balance"]]

Describe alternatives you've considered
N/A

Additional context
Should behave similar to ODFV and Stream Feature Views and support Python and Pandas.