issue: https://github.com/milvus-io/milvus/issues/45006
ref: https://github.com/milvus-io/milvus/issues/42148
Previsouly, the parquet import is implemented based on that the STRUCT
in the parquet files is hanlded in the way that each field in struct is
stored in a single column.
However, in the user's perspective, the array of STRUCT contains data is
something like STRUCT_A:
for one row, [struct{field1_1, field2_1, field3_1}, struct{field1_2,
field2_2, field3_2}, ...], rather than {[field1_1, field1_2, ...],
[field2_1, field2_2, ...], [field3_1, field3_2, field3_3, ...]}.
This PR fixes this.
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Signed-off-by: SpadeA <tangchenjie1210@gmail.com>
