Mediation and transports

[TimoGlastra]

Opening a discussion here to see how we can improve the architecture for mediation and transports for the long-term. It works fine, but would be good to remove some transport specific code from the modules

[TimoGlastra]

https://github.com/TimoGlastra/aries-framework-javascript/blob/b17d57f7bdd2e18ae1e6501033f8d10e5c7bade8/packages/core/src/modules/routing/RecipientModule.ts#L76-L86

Shouldn't those methods be part of the transport layer rather than inside the core of the framework? Or, it's just temporary?

Originally posted by @jakubkoci in #432 (comment)

[TimoGlastra]

What it does is sending a trust ping message with a restriction to only use websocket. The websocket will be kept alive autmoatically (I'd like to make the keep alive more explicit)

I'm not sure yet how we could nicely integrate this into the transport layer. Would be nice to not make it WebSocket specific (so just send a ping and keep the socket alive), but we need to specify somewhere which transports are capable of this, as e.g. HTTP isn't.

Maybe a transport should be able to specify whether it can send multiple messages (WebSocket is ∞, while HTTP is 1 request, 1 response). That way we wouldn't have to specify WS explicitly, but rather whether we want a transport that can stay open (for implicit pickup)

I'm going to think about it for a while. We can have a discussion about it in the WG call