Cover AdditionalExpectedResponses as error responses

[relu91]

Current TD specification introduced the concept of additionalResponses to model APIs that might return different payloads from the same affordance. This issue focuses on AdditionalExpectedResponses marked with the field success: false (default). The goal is to understand how to treat these responses in our runtime. The discussion is strongly connected with #200.

[relu91]

Call 11/12:

• @relu91 As a draft idea we can just instruct runtimes to throw one general OperationError
• Should we throw or return the error?
• @JKRhb Introduce a custom error type to wrap the error and access it with a value function.
• @ashimura we should talk about error handling in general in overall Scripting API, depending on potential responses.