add the sql UDF function for calculating percentile

add the percentile for all input values of x at the given percentage
@lumianph

Look for existing SQL UDF functions in the codebase to understand the pattern. The function likely needs to be added to the SQL engine's function registry. Check the documentation for adding UDFs and test the percentile calculation with sample data. Verify the implementation works for all input values of x at the given percentage.

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