Change transport type preference

[jdknives]

Feature description

When calling skywire-cli visor add-tp $PubKey without specifying the transport type explicitly, the visor should try to establish an stcp transport by default and only establish a dmsg transport once that fails. (As soon as we implemented a holepunch transport, this type should be setup before trying dmsg setup.)

Is your feature request related to a problem? Please describe.
Using an stcp transport is preferable when that is possible. However, it is not clear for a visor whether establishing an stcp transport is possible, given that the other visor could be behind a NAT. So either we would have to somehow exchange information about the remote visor's network properties or we just attempt to establish transports in the prefered order until transport establishment is successful. The latter option seems more straightforward for now.