Add server list ping

[kai-gitt]

Temporarily built into the server itself, will be transformed into a plugin later when the actual plugin system comes.

Example configuration of the motd

{
      // ... rest of config ...
      "server": {
        "motd": "An Arciera Server",
        "favicon": "./assets/icon.png",
        "enforcesSecureChat": false,
        "maxPlayers": 100,
        "version": {
            "name": "Arciera 1.20.1",
            "protocol": 763
        }
    }
}