Allow for disabling AutoNat

[p-shahi]

AutoNat need not run as a default libp2p service, we should either disable it by default or allow for disabling it.
Ref: libp2p/universal-connectivity#45

[achingbrain]

Agree that you should be able to disable it in the name of smaller surface areas for attacks, but what's the problem autonat is causing?

[maschad]

Closed in https://www.github.com/libp2p/js-libp2p/issues/1563