The `conversation.Message` structure does not return the `error` substructure.

[krzysztofreczek]

When there is a message with a rejected status, the GET /v1/messages/:id endpoint returns an error substructure with a detailed error description as you can see in the screenshot below:

Unfortunately, the error substructure is not available in the Go client conversation.Message payload:

go-rest-api/conversation/message.go

Line 84 in e0a41ed

type Message struct {

Is this missing, or is there another recommended method of retrieving the error details using the Go client?