Optional LiveKit credentials for AvatarSession.start; falls back to env vars.
Optional
LiveKit API key. Falls back to LIVEKIT_API_KEY.
LIVEKIT_API_KEY
LiveKit API secret. Falls back to LIVEKIT_API_SECRET.
LIVEKIT_API_SECRET
LiveKit server URL. Falls back to LIVEKIT_URL.
LIVEKIT_URL
Optional LiveKit credentials for AvatarSession.start; falls back to env vars.