[Feature][SDK] Transform Support ELT Function

[ying-hua]

Description

• parent [Umbrella] Tencent Rhino-bird: Expand InLong Transform functions #10796
• flinkSql doc: https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/functions/systemfunctions/
• ELT(index, expr[, exprs]*)
  Returns the index-th expression. index must be an integer between 1 and the number of expressions.
  Retuens NULL if index is NULL or out of range.

Use case

No response

Are you willing to submit PR?

• Yes, I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct