Add enable_user_notifications config option to Invidious
This will allow you to toggle `enable_user_notifications` on or off
(default on) via https://github.com/iv-org/invidious/pull/3473⚒️ Fixes #13125
- [x] ⚙️ Feature/App addition
- [ ] 🪛 Bugfix
- [ ] ⚠️ Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] 🔃 Refactor of current code
**🧪 How Has This Been Tested?**
Installed the helm chart locally with no errors
**✔️ Checklist:**
- [x] ⚖️ My code follows the style guidelines of this project
- [x] 👀 I have performed a self-review of my own code
- [ ] #️⃣ I have commented my code, particularly in hard-to-understand
areas
- [ ] 📄 I have made corresponding changes to the documentation
- [x] ⚠️ My changes generate no new warnings
- [x] 🧪 I have added tests to this description that prove my fix is
effective or that my feature works
- [ ] ⬆️ I increased versions for any altered app according to semantic
versioning
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