feat: add UPnP NAT manager (#810)

* feat: add uPnP nat manager

Adds a really basic nat manager that attempts to use UPnP to punch
a hole through your router for any IPV4 tcp addresses you have
configured.

Adds any configured addresses to the node's observed addresses list
and adds observed addresses to `libp2p.multiaddrs` so we exchange
them with peers when performing `identify` and people can dial you.

Adds configuration options under `config.nat`

Hole punching is async to not affect start up time.

Co-authored-by: Vasco Santos <vasco.santos@moxy.studio>

doc/API.md

@@ -2055,6 +2055,15 @@ This event will be triggered anytime we are disconnected from another peer, rega
 - `peerId`: instance of [`PeerId`][peer-id]
 - `protocols`: array of known, supported protocols for the peer (string identifiers)
 
+### libp2p.addressManager
+
+#### Our addresses have changed
+
+This could be in response to a peer telling us about addresses they have observed, or
+the NatManager performing NAT hole punching.
+
+`libp2p.addressManager.on('change:addresses', () => {})`
+
 ## Types
 
 ### Stats