servlet: introduce ServletServerBuilder.buildServlet() - #10921

@Bean
public ServletRegistrationBean<GrpcServlet> myServiceServlet(MyServiceImpl serviceImpl) {
    GrpcServlet servlet = new ServletServerBuilder()
            .addService(serviceImpl)
            .intercept(TransmitStatusRuntimeExceptionInterceptor.instance())
            .buildServlet();
    return new ServletRegistrationBean<>(servlet, "/" + MyServiceGrpc.SERVICE_NAME + "/*");
}