[FEATURE] Expose custom bindings

[rossdanderson]

Why do we need this improvement?

From the documentation https://www.asyncapi.com/docs/reference/specification/v3.0.0#channelBindingsObject - it appears that the Binding Object should be extendable.
When deserializing a specification the map contains a null Object in the getBindings map which, as someone wanting to produce a custom binding, makes life a bit more difficult.

How will this change help?

A user of the library will be able to access their binding extensions, and deserialize them to the appropriate type more simply.

Screenshots

channels:
  fxConfig:
    address: /PRIVATE/FX/CONFIG
    bindings:
      x-datasource:
        map:
          - value: "%u"
            position: 2
    description: Channel for FX user config
    messages:
      FXConfigMessage:
        $ref: "#/components/messages/FXConfig"

fun main() {
    val objectMapper = ObjectMapper(YAMLFactory())

    val api = objectMapper.readValue<AsyncAPI>(object {}::class.java.getResourceAsStream("/userconfig/asyncapi.yaml"))

    api.channels?.forEach { (channelName, channel) ->
        check(channel is Channel)

        println(channel.bindings)
    }
}

outputs:

{x-datasource=null}

How could it be implemented/designed?

It would be nice if it provided a JsonNode, or a Map like Channel#getExtensionFields in the case where it encounters an extension? It looks like this might be a simple change to ChannelBindingsDeserializer (and likely the other binding deserializers).

default: return jsonParser.readValueAs(JsonNode.class);

I do not know if this is a breaking change or not as there may be code that depends on binding extensions being null in order to ignore them.

🚧 Breaking changes

Yes

👀 Have you checked for similar open issues?

• [X] I checked and didn't find a similar issue

🏢 Have you read the Contributing Guidelines?

• [X] I have read the Contributing Guidelines

Are you willing to work on this issue?

Yes I am willing to submit a PR!

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[Pakisan]

@rossdanderson hi! Thanks, will check your proposal, on weekends