Create option for custom levels

[xopr]

Implement metadata to facilitate custom levels/rooms

Note that the limit for both room and participant is 64kB:

• https://docs.livekit.io/transport/data/state/room-metadata/
• https://docs.livekit.io/transport/data/state/participant-attributes/

Some ideas:

room metadata
  level
    background
    overlay
    bounds
    spawnpoints[]
  objects[]
    image
    activeImage
    action: audio, video, audioStream, videoStream, website, backendCall..?

Some links for map making:

• https://gathertown.fandom.com/wiki/Mapmaking_Resources
• https://github.com/puifine/mapmaking (old fork: https://github.com/iamthad/gathertown-mapmaking )