`console` / `wireguard`: add support for network

[Tailzip]

fly doesn't support setting --network flag for fly console and fly wireguard like it does for fly apps create. Therefore, it's impossible to connect to machines' 6PN address if launched in a custom network.

It looks like GraphQL API support for creating wireguard peer in given network exists:

input AddWireGuardPeerInput {
  # [...]

  # Network ID to attach wireguard peer to
  network: String

  # [...]
}

For reference, support for apps has been added in #563.

[owenthereal]

I just ran into this issue and couldn't ssh into an app with an isolated network. Even better, I would auto-detect the network for fly ssh console because AFAIK an app can only have one network.