Adding the document-new entry Context Managers and files

[Maet22]

Description

Adding an entry that explains the concept of context managers and introduces the ways to use concept managers with files.

Issue Solved

It was not related to an existing issue.

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.