Allow to use peers as relays to access to another peers behind NAT

[pymq]

For now only community bootstrap nodes can be used as relays (they announce themselves as relays). But we can add more clever thing: allow you to use your friendly devices as a relay for you. This feature will make awl truly mesh vpn.

How this will work. For instance, you have 3 devices: server 1 with public IP, server 2 without public IP and your laptop, they all know each other. Because server 1 have public IP, you can connect to server 2 from your laptop via server 1.

More technically:

• there should be new config option like Allow to use my device as relay for known peers. By default it's false
• a new option must be passed to p2p here. Option like libp2p.EnableRelayService(relay.WithResources(relayResourcesCfg), relay.WithACL(TODO)). Important part is ACL - we must allow it only for known peers and only if peer enabled config option above
• there must be new test here

[dillfrescott]

Great idea!