fix: introduce submenu logic in Conversation component

[Antreesy]

☑️ Resolves

• Fix Reintroduce notification radio in the conversation menu  #13176
• No-whitespaces diff: https://github.com/nextcloud/spreed/pull/13862/files?w=1

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

🏚️ Before	🏡 After
no

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • 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

[DorraJaouad]

All good, as it follows same structure and logic in conversation settings.

[Antreesy]

/backport to stable30