Add support for routing messages based on attribute decoration

[patchoulish]

Is your feature request related to a problem? Please describe.
I'd like to decorate messages I want to wind up in a certain queue with an attribute, rather than use a marker interface.

Describe the solution you'd like
Something like the following

options
    .Publish(rule =>
    {
        rule.MessagesDecoratedWith<MySpecificQueueAttribute>()
            .ToPostgresqlQueue("my-specific-queue");
    });

Describe alternatives you've considered
Marker interfaces offer essentially the same functionality as what I'm looking for.

[jeremydmiller]

@patchoulish The associated PR needs an integration test that actually uses the publishing rule up above. I think I want you to hold off on the implementation anyway. I think there's probably a more usable way to accomplish this.

[patchoulish]

@jeremydmiller Sure thing! I can write an integration test and some documentation for the existing solution, or re-implement the feature differently and do the same once you've thought on it more. Just give me a heads up.