[Docs] Add documentation for complex type mapping between Flink and Fluss

[wuchong]

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Description

https://fluss.apache.org/docs/next/engine-flink/getting-started/#type-conversion

We need to add the mapping for the new introduced types: ARRAY, MAP, ROW

Willingness to contribute

• I'm willing to submit a PR!

[jeyhoun]

Hi, I would like to work on this issue. Thanks!