Mostly for SS13 hub. Custom hub address for world can allow more credibility for listed servers, and in some way be like verification for community owned servers.

1. This address should be used in hub (web version and pager) instead of generated byond://BYOND.world.numbers
2. Can be IP or domain name with port, ex. 1.1.1.1:1111, domain.com:1111
3. This address should be visible in pager, clients need to see where they are connecting. Currently it's only true for web version.
4. Client should use this address for connection from hub and pager, so it should not be possible to be listed in hub with someone else's address and still be accessible through default address.

This can be DreamDaemon parameter, maybe something like -world_address

Or, as hub is already managed by world object https://www.byond.com/docs/ref/info.html#/world/var/hub, be world variable like hub_address. But it should be possible to change var at runtime, so we can set this from config.