* Improve service response data APIs
Make the API naming more consistent, and require registration that a
service supports response data so that we can better integrate with
the UI and avoid user confusion with better error messages.
* Improve test coverage
* Add an enum for registering response values
* Assign enum values
* Convert SupportsResponse to StrEnum
* Update service call test docstrings
* Add tiny missing full stop in comment
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Co-authored-by: Franck Nijhof <frenck@frenck.nl>