Add compatibility test for $percentile (second pass)

[eerxuan]

Part of #19.

Category: core / operator / expressions / accumulator

Add compatibility test coverage for the $percentile expression operator.

[ramaiyaKushal]

Hi, I would like to take this issue!

[Kwadwot]

Hi, I am a student in the CodePath AI301 course. I am interested in working on this issue if it has not been claimed or assigned.

I understand that contributing to this particular issue entails writing a good compatibility test in Python for the $percentile accumulator expression operator. After skimming the CONTRIBUTING.md file, I believe I can implement the test for the expression operator after cloning, setting up a MongoDB instance, and reviewing and testing the relevant files.