[Term Entry] Subject: SQL Equal to operator

[selenahuang017]

Description

Adding SQL Equal to operator to SQL concepts under docs/content/sql/concepts/operators/terms/equal-to/equal-to.md. Addresses issue: #4849

Type of Change

• Adding a new entry

Checklist

• 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.
• 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.