Support `http` to `kafka` proxy using `openapi.yaml` and `asyncapi.yaml`

[jfallows]

Describe the desired outcome from the user's perspective
As an OpenAPI and AsyncAPI consumer, I want to configure zilla as http proxy to kafka using openapi.yaml and asyncapi.yaml more directly in zilla.yaml.

Acceptance criteria

• openapi server binding configured via openapi.yaml
• openapi-asyncapi proxy binding configured via openapi.yaml and asyncapi.yaml
• asyncapi client binding configured via kafka asyncapi.yaml
• only openapi server, openapi-asyncapi proxy, and asyncapi client bindings needed to configure http to kafka proxy

Additional context
Syntax similar to the following in zilla.yaml using composite bindings.

bindings:
  openapi_server:
    type: openapi
    kind: server
    options:
      specs:
        - http/openapi.yaml
    exit: openapi_asyncapi_proxy
  openapi_asyncapi_proxy:
    type: openapi-asyncapi
    kind: proxy
    options:
      specs:
        - http/openapi.yaml
        - kafka/asyncapi.yaml
    routes:
      - when:
          - operation: ... # openapi operation id
        exit: asyncapi_client
        with:
          operation: ... # kafka asyncapi operation id
  asyncapi_client:
    type: asyncapi
    kind: client
    options:
      specs:
        - kafka/asyncapi.yaml