AsyncAPI http-kafka header overrides support

[jfallows]

Add support for http-kafka header overrides.

Example:

operations:
  doStreampayPayCommand:
    action: send
    channel:
      $ref: '#/channels/streampay-pay'
    bindings:
      http:
        method: POST
      x-zilla-http-kafka:
        overrides:
          zilla:domain-model: PayCommand
          zilla:identity: {identity}
    messages:
      - $ref: '#/channels/streampay-pay/messages/StreampayPay.message'

results in

    routes:
      - when:
          - method: POST
            path: /pay
        exit: kafka_cache_client0
        with:
          capability: produce
          reply-to: replies
          topic: commands
          key: ${idempotencyKey}
          overrides:
            zilla:domain-model: PayCommand
            zilla:identity: ${guarded['<guard-name>'].identity}