fix(chat-relay): mark experimental flag completed

[Antreesy]

☑️ Resolves

• Follow-up to fix: mark experimental flags completed on main branch (Nc 33) #16629
  • Resolve once it's done - EXPERIMENTAL.CHAT_RELAY - Initially planned for 23.0.0

🖌️ UI Checklist

🚧 Tasks

• Finish translations
• Resolve fallback polling
• ...

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • Integrations with Files sidebar and other apps
  • Not risky to browser differences / client
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

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🛠️ API Checklist

🚧 Tasks

• ...

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not possible
• 📘 API documentation in docs/ has been updated or is not required
• 🔖 Capability is added or not needed