[New Entry] Added SQL SUBSTRING function

[sebasmagno007]

Description

Added a New Entry term for SQL string functions and created the topic SUBSTRING. My motivation is to contibute to Codeacademy docs in the topics that I am learning.

Issue Solved

Closes #4960

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.

[CLAassistant]

All committers have signed the CLA.

[cigar-galaxy82]

Hi @sebasmagno007 thank you for contributing to Codecademy docs, the entry is well written, I have suggested a few changes please modify

[sebasmagno007]

Hi, @cigar-galaxy82 . The changes have been made.

[github-actions[bot]]

👋 @sebasmagno007 You have contributed to Codecademy Docs, and we would like to know more about you and your experience. Please take a minute to fill out this four question survey to help us better understand Docs contributions and how we can improve the experience for you and our learners. Thank you for your help!

🎉 Your contribution(s) can be seen here:

https://www.codecademy.com/resources/docs/sql/string-function/substring https://github.com/Codecademy/docs/blob/main/documentation/tags.md

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