Support AsyncAPI v2 for `http-kafka` mapping

[jfallows]

Describe the desired outcome from the user's perspective As an AsyncAPI author, I want to be able to use Zilla to map http to kafka using AsyncAPI v2 syntax.

Acceptance criteria

• Successfully maps AsyncAPI v2 http spec to AsyncAPI v2 kafka

Additional context No hard dependency on AsyncAPI v3 new features, so excluding request-response, just CRUD style.