Add missing OSS release notes

[NoyaOffer]

• Added release notes files for v0.20.0 through v0.16.0
• Formatted in the same style as existing release notes (0.17.0, 0.18.0)
• Includes user-friendly summaries with emojis and links to GitHub releases

[coderabbitai]

Important

Review skipped

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch add-missing-release-versions-to-changelog

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