[Term Entry] Python:Pandas dataframe at #4520

[aSagCoder]

Description

• Created a new branch in order to make merging easier for the given term entry. Has already undergone two reviews and just needs to get merged into the main branch.
• Added the .at[] function for Pandas.
• Can be located here - docs/content/pandas/concepts/dataframe/terms/at/at.md.

Issue Solved

Closes #4520

Type of Change

• Adding a new entry
• ~~Editing an existing entry (fixing a typo, bug, issues, etc)~~
• ~~Updating the documentation~~

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.