Create quantile entry in NumPy

[tgowan1]

Description

Created a new entry for .quantile() under built-in functions in NumPy. The entry is located in docs/content/numpy/concepts/built-in-functions/terms/quantile/quantile.md.
This is for open issue #6415, and part of a project in the Learn Git & GitHub module.

Issue Solved

Closes #6415

Type of Change

• Adding a new entry

Checklist

• [x ] All writings are my own.
• [x ] My entry follows the Codecademy Docs style guide.
• [x ] My changes generate no new warnings.
• [x ] I have performed a self-review of my own writing and code.
• [x ] I have checked my entry and corrected any misspellings.
• [x ] I have made corresponding changes to the documentation if needed.
• [x ] I have confirmed my changes are not being pushed from my forked main branch.
• [x ] I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• [x ] I have linked any issues that are relevant to this PR in the Issues Solved section.

[CLAassistant]

All committers have signed the CLA.

[mamtawardhani]

I'll have to close this PR as another author has been assigned to this issue.
@tgowan1 Please make sure that for future contributions, you first ask to be assigned to an issue - once assigned, then you can raise a PR for that.
Thank you! 😄