Support Sql transformation

[HaoXuAI]

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Reference: https://docs.tecton.ai/docs/defining-features/feature-views/transformations

[nquinn408]

Maybe something like this:

spark_transformation = Transformation(
    mode=TransformationMode.SPARK_SQL,
    sql="SELECT sum(total_cost) FROM jetpack_purchase",
)
feature_view = FeatureView(
  source=[jetpack_purchase],
  feature_transformation=spark_transformation,
  ...
)

[nquinn408]

But I guess you need to pass in the dataframe jetpack_purchase so it would need to be a function.