Fix a few navless database development guide docs

What does this MR do and why?

Fix a few navless database development guide docs

• add to nav

Screenshots, screen recordings, or links to review app

How to set up and validate locally

• https://fix-toc-items.docs.gitlab-review.app/ee/development/database/not_null_constraints.html
• https://fix-toc-items.docs.gitlab-review.app/ee/development/database/query_performance.html

Merge request acceptance checklist

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• I have evaluated the MR acceptance checklist for this merge request.