Check if the schema contains timestamp field if timestamp_field is not None

[jiangxin369]

Currently, we can construct a Source with timestamp_field set but not contained in the schema like the following test. We should raise an exception in Feathub instead of failing until submitting to a processor.

    def test_get_output_fields(self):
        field_names = ["id", "val1", "val2", "val3"]
        source = DataGenSource(
            name="source_1",
            schema=Schema(field_names, [Int64, Int64, Int64, Int64]),
            timestamp_field="lpep_dropoff_datetime",
            timestamp_format="%Y-%m-%d %H:%M:%S",
            keys=["id"],
        )

        feature_view_2 = DerivedFeatureView(
            name="feature_view_2",
            source=source,
            features=["val2", "val3"],
            keep_source_fields=False,
        )

        built_feature_view_2 = feature_view_2.build(self.registry)

        if isinstance(built_feature_view_2, FeatureView):
            self.assertEqual(
                ["lpep_dropoff_datetime", "id", "val2", "val3"],
                built_feature_view_2.get_output_fields(field_names),
            )
        else:
            raise Exception("FeatureView is expected.")