Redesign REST service to URL mapping

[demonfiddler]

The present service : URL mapping in openapi.yaml is sub-optimal and contains anti-patterns copied from the flawed OpenAPI PetStore example. For instance, REST best practice states that verbs should be reflected in the HTTP request type, not in request URI path segments or query parameters, but the present design does just that. These anti-patterns should be eliminated and replaced by best practice patterns.