Closes #7134 : Added a new entry for swap() method under strings in C++.

[roshnianand1710]

Description

I added a new entry for swap() method under strings in C++. The entry is in content/cpp/concepts/strings/terms/swap/swap.md
Motivation : I am new to open source and I want to become an active open source contributor by adding value wherever I can and always learning new things!

Issue Solved

Closes #7134

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.

[CLAassistant]

All committers have signed the CLA.

[mamtawardhani]

Hey @roshnianand1710 please also add an ##Example section above codebyte example section