Override @c SubscriptionAdminClient Default Endpoint

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