Allow Error return customization

**Is your feature request related to a problem? Please describe.**
We have the need to customize Error responses, e.g.: Add an Error Code/Status Code. And we feel that it's kind of limiting to only have `messages.InvokeResponse_Error{}` as Error Return.

**Describe the solution you'd like**
Is it possible to make this customizable via Custom JSON Serialization ?

**Describe alternatives you've considered**
N/A

**Additional context**
N/A

The issue names no files or tests. Start by locating the messages.InvokeResponse_Error path and the custom JSON serialization entry points in this Go repository. Clarify the customization contract and define tests for configurable error and status codes; done requires an agreed behavior with passing coverage.

Scritto dal modello di indicizzazione a partire dal testo della issue.