chore: upgrade api7 and gateway to v3.9.16

[jarvis9443]

Upgrade the API7 and Gateway charts for the 3.9.16 release.

This bumps chart app versions and image tags to 3.9.16, regenerates chart READMEs, and exposes the new gateway runtime settings for encoded slash matching, POST args readable size, and trusted forwarded-header addresses.

[coderabbitai]

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/upgrade-3.9.16

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