public GrpcHealthCheckServiceBuilder serviceCheckers(String serviceName,
                                                         ListenableHealthChecker healthChecker) {
        grpcHealthCheckers.put(requireNonNull(serviceName, "serviceName"),
                               requireNonNull(healthChecker, "healthChecker"));
        return this;
    }
Adds the pair of the service name and the {@link ListenableHealthChecker} that determine
the healthiness of the specified gRPC service.
The specified health checker is not used for determining the healthiness of the {@link Server}.

<p>Note: The suggested format of service name is `package_names.ServiceName`.
For example, If the proto package that defines `HelloService` belongs to `com.example`,
the service name is `com.example.HelloService`
grpc/src/main/java/com/linecorp/armeria/server/grpc/GrpcHealthCheckServiceBuilder.java