Add extend() for collections.deque in python

[Aaravthk]

Description

Added a new entry for the extend() method under the collections.deque module in Python.
This entry provides a description of the method, its syntax, an example demonstrating its use, and a runnable Codebyte example.

Issue Solved

Closes #7749

Type of Change

• Adding a new entry

Checklist

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

[mamtawardhani]

Hey @Aaravthk, can you please remove the pop.md file from this branch? Other things look good!

[mamtawardhani]

@Aaravthk are you working on this? Otherwise we'll have to close the PR

[Aaravthk]

I am travelling right now, I will modify the files tomorrow if that works?