[Feature] Integrate LiveKit for meetings

[evereq]

In addition to existing https://jitsi.org integration, we would like to also integrate (optionally, i.e. by user selection) https://livekit.io.
Essentially LIVEKIT_xxx env vars should be possible to define (API_KEY, API_SECRET, URL) and if they are not empty, we should use LiveKit for meetings.

We should use packages: "@livekit/components-react" and "@livekit/components-styles" and have meeting rooms etc.