Support UPnP

[dknopik]

Lighthouse supports UPnP for automatic port forwarding, we should as well. :)

[petarjuki7]

HI!

I'd like to try to work on this if it's okay.

A few questions looking at the Lighthouse implementation, should we also have a function to update the ENR ports on the libp2p::upnp::Event::NewExternalAddr event?
Also, add a config flag to toggle upnp on or off?

[dknopik]

Hey 👋

Yeah, feel free to work on this!

Currently, we do not update our own ENR, but this is just because it is not implemented yet:

• Update ports in ENR #255

It probably makes sense to have those in separate PRs, so feel free to not update the ENR ports yet until #255 is implemented.

Yep, a --disable-upnp flag like in Lighthouse would be perfect.

Thank you for helping out! Let me know if you have any other questions.