[Concept Entry] Subject: performance tuning in sql

[SaviDahegaonkar]

Description

Added a new concept entry on the Performance Tuning in SQL

Issue Solved

#4883

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.

[dakshdeepHERE]

This LGTM and I think we can create term entries on this but will have to discuss about this.

[github-actions]

👋 @SaviDahegaonkar
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