fix: enable cache only for clientDb

[Barbapapazes]

🔗 Linked issue

fix #2415

❓ Type of change

• [ ] 📖 Documentation (updates to the documentation or readme)
• [x] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [ ] 👌 Enhancement (improving an existing functionality like performance)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Enable the /api/cache.json endpoint only for the clientDb feature. Otherwise, it's unnecessary and can be a real pain (build perf and deployment) for huge website.

📝 Checklist

• [ ] I have linked an issue or discussion.
• [ ] I have updated the documentation accordingly.

[farnabaz]

Disabling it has side effect. What we can do for now is to add a flag to disable it. In next major version, this behavior will change, and we will remove this big chunk.