Allow arbitrary additional props to be passed to `createError`

[hymair]

Describe the feature

I want to send an additional prop in my error responses. For example code: "invitation_not_found" and I don't want it to be under data, but in the root error object.

Additional information

• [ ] Would you be willing to help implement this feature?

[RobertHaba]

I have similar expectations about putting additional information in the root. Any updates?

[pi0]

Latest v2 will allow new HTTPError({ body: {} }) to add more keys to top level of JSON response object.