callview: Show internal clients with available video.

[fancycode]

☑️ Resolves

• Shows video component for internal (SIP-) clients that publish a video stream.

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

🏚️ Before	🏡 After
Screenshot before	Screenshot after

🚧 Tasks

• ...

🏁 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