[SPARK-39030][PYTHON] Rename sum to avoid shading the builtin Python function
[SPARK-39030][PYTHON] Rename sum to avoid shading the builtin Python function

### What changes were proposed in this pull request?
Rename sum to something else.

### Why are the changes needed?
Sum is a build in function in python. [SUM() at python docs](https://docs.python.org/3/library/functions.html#sum)

### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?
Use existing tests.

Closes #36364 from bjornjorgensen/rename-sum.

Authored-by: bjornjorgensen <f1cf9edeb432464e844067a8928e544915acf114@gmail.com>
Signed-off-by: Hyukjin Kwon <2680965ad5aae29275c8fb10150cb10f5554e78b@apache.org>
(cherry picked from commit 3821d807a599a2d243465b4e443f1eb68251d432)
Signed-off-by: Hyukjin Kwon <2680965ad5aae29275c8fb10150cb10f5554e78b@apache.org>

milliman/spark,milliman/spark,milliman/spark,milliman/spark,milliman/spark,milliman/spark,milliman/spark