[Edit] C++ Strings: insert()

[Kunalkudande]

Description

This PR adds a new Docs entry for the C++ .insert() method under content/cpp/concepts/strings/terms/insert/insert.md.
The entry explains the usage of the .insert() method for strings in C++, including:

• A clear description of its purpose
• A dedicated ##Syntax section covering all overloads
• Example use cases in plain code
• A live Codebyte example using codebyte/cpp for interactive execution

This entry follows the structure and style of the .append() term entry for consistency.

Issue Solved

Closes #7136

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 @Kunalkudande you'll have to raise a new PR as this one is raised from the main branch. Can you please create a feature branch, edit on the feature branch and raise a PR?
Thank you! 😄