Support Column Names in Fluss DS Sink for Partial-Updates

[polyzos]

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Description

Currently the Fluss Sink for the datastream API supports target columns for partial-updates, but columns are specified via indexes.
We want to update the sink, so it can use column names instead of indexes since it is more user-friendly

Willingness to contribute

• I'm willing to submit a PR!

[polyzos]

908 needs to be merged first

[MehulBatra]

@polyzos I will take care of it

[wuchong]

@polyzos sorry, what is "projection pushdown for sink"? Do you mean partial update which only updates specific columns?

[litiliu]

Seem the DataStream API still doesn't support partialUpdateColumns?
https://github.com/apache/fluss/pull/908/files#diff-f4fe567c94d882d4d9afad54a103c98f80bd9a96ecd3df7fc7cf52d16c985c88R160

[polyzos]

@litiliu yeah, we should add this functionality. The goal was to introduce it in a separate PR, which seems like it was forgotten.
Thanks for reminding me

[polyzos]

@litiliu I created a PR #2042