Improve Public IP address handling

[rolznz]

Currently we are broadcasting we are connectable on localhost addresses, which is bad (because from the outside this is not possible). We do this to make sure our node can be peered to (for our tests with IPv6 IPs on Fly)

• Allow IP address to be passed to Alby Hub on startup - if not provided, we should not set config.ListeningAddresses in LDK.
• Display connection string in UI so user can share it with person/service who would like to peer

From LDK:

I mean you have to decide whether you're running public routing nodes (with announced channels) or not. You can't just listen and announce wildcard IPs. If you're opening announced channels it means "these can be used for routing" and you need to provide valid addresses under which these nodes are reachable

From Olympus:

Your node is broadcasting that it is connectable @ local hosts like 0.0.0.0 and [::]

CC @bumi

[bumi]

So let's do this through the env variable