code: public static HealthCheckRegistry setDefault(String name, HealthCheckRegistry healthCheckRegistry) {
          if (defaultRegistryName.compareAndSet(null, name)) {
              add(name, healthCheckRegistry);
              return healthCheckRegistry;
          }
          throw new IllegalStateException("Default health check registry is already set.");
      }
docs: Sets the provided registry as the default one under the provided name
  
  @param name                the default registry name
  @param healthCheckRegistry the default registry
  @throws IllegalStateException if the default registry has already been set