WebRTC signaling servers cannot be reached

[almereyda]

Describe the bug

Intruige uses the embedded URLs for the signaling servers, of which many have disappeared or do not have a CSP configuration which would allow usage.

This results in failing connections between peers.

To Reproduce

1. Open a board and its developer tools
2. Open it in a private browser windows
3. See errors appear in the console and in the network tab

Expected behavior

There are no errors and the clients are synced.

Additional context

It's best to run one's own signalling server. The demo instance is known to be weak and not for productive use. There are two known options, the JS one and another in Rust linked from yjs/y-webrtc#55