Construct publisher/subscriber from DSN like URLs

[sagikazarmark]

I think it would be nice to have a quick way to construct publishers/subscribers, similarly to https://gocloud.dev/concepts/urls/

That would allow configuring Watermill with DSNs like nats:// or amqp:// from config files or env vars.

Dependency is probably a question though. It could work similarly to how SQL driver registration works by simply importing the relevant packages.