code: @DeleteMapping(path = "/instances/{id}")
      public Mono<ResponseEntity<Void>> unregister(@PathVariable String id) {
          LOGGER.debug("Unregister instance with ID '{}'", id);
          return registry.deregister(InstanceId.of(id))
                         .map(v -> ResponseEntity.noContent().<Void>build())
                         .defaultIfEmpty(ResponseEntity.notFound().build());
      }
docs: Unregister an instance
  
  @param id The instance id.
  @return response indicating the success