Add support for aggregate functions like `list_agg` return complex data types

[wuchong]

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Description

Add support for list_agg aggregate functions that returns complex data types.

Willingness to contribute

• I'm willing to submit a PR!

[Prajwal-banakar]

Hi @wuchong I’ve implemented the support for aggregate functions over complex types. However, the CI is currently failing on FlinkUnionReadPrimaryKeyTableITCase.