Scout selectively regarding transports

[OlivierHecart]

Describe the feature

It is right now possible to scout for routers, clients, peers or any combination of them. It would be good to be able to scout for processes that support given transports (especially since #443). It does not make much sense to scout remote processes that only support transports not supported by the local process. Typically a process using TLS would want to only scout for processes supporting TLS.