Update CHANGELOG.md with ngram changes

[matthewmcneely]

This is simply an update to the change log

[Copilot]

Pull Request Overview

This PR updates the CHANGELOG.md file to document recent ngram functionality additions. The changes add entries for new ngram features in both the Core and GraphQL components.

• Adds changelog entries for ngram (shingles indexing and search) functionality
• Documents both Core DQL and GraphQL ngram search features
• References PR #9463 for both feature additions

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