suggestion: make utp-native as an option

[gitawego]

as we are behind company proxy, we neither can download utp-native binary, nor build when installing.
I'd suggest make utp-native as an option when instantiating hyperswarm (for @hyperswarm/network), so we can download manually utp-native, and provide to hyperswarm via an option. such as:

const swarm = hyperswarm({
   utpProvider: our-predownloaded-utp-native
})

Thanks a lot.