Override @c BlockingPublisher Default Endpoint

  namespace pubsub = ::google::cloud::pubsub;
 
using ::google::cloud::Options;
 
[]() {
   
return pubsub::BlockingPublisher(pubsub::MakeBlockingPublisherConnection(
       
Options{}.set<google::cloud::EndpointOption>(
           
"private.googleapis.com")));
 
}