Decided to create this PR after discussing with @zivkovicmilos.

This PR changes the default listening address for the RPC node and gnoweb to be 0.0.0.0 instead of 127.0.0.1. This entails that when starting up a gno.land node or a gnoweb server, it is accessible from any IP address (on the specified port). This includes local loopback addresses like 127.0.0.1, private network addresses like 192.0.0.X, public addresses if the machine has one and the ports are not firewalled, as well as giving the ability to expose the services in docker without having to juggle flags or configuration files.

Milos: What do you think about changing the default IP to 0.0.0.0?
In the code itself, always

Morgan: that is an option and my first thought
but I think there could be security concerns
ie. the RPC node could be an attack vector a validator might not want to expose by default, so it makes sense to expose it only with an opt-in

Milos: I have never in my life seen a production blockchain node directly exposed to the internet
without something like nginx in front of it
There are entire layers of issues that don't have to be solved node-level
The protocol can't cover everything, and it shouldn't
I'd 100% back having the default listen address 0.0.0.0
There is no argument against it really, because the node won't ever be "naked" on the internet

This PR attempts to improve the developer experience of using the two services "by default", with the risk of exposing the RPC endpoints out-of-the-box which could be undesirable for some production environments. However, as Milos has stated, and I agree, any validator who wants to launch a production-grade node

1. without having a firewall already set up on their system
2. without checking through the configuration and defaults for the gnoland node
3. without putting a reverse-proxy like nginx, caddy, $what_have_you
4. expecting that this does not expose the RPC endpoint by default

... is probably insane.

cc/ @albttx