fix: polish writing service error responses

[babakks]

This PR polished the way we map errors thrown by services (e.g., IdentitiesService) to the OpenAPI spec response type.

This PR also:

• Removes the unused delegateErrorResponseMapper type and applies the same approach within the mapServiceErrorResponse function.
• Drops unused skip variable from table tests.
• Fixes handler struct instantiation by providing it with all services.
• Adds explicit Content-Type: application/json header to responses.
• Improve some field names by removing the Service suffix.

Fixes CSS-7635