message: fix: add getSubscriberStub to synth file
diff: @@ -31,6 +31,9 @@ s.replace("src/v1/subscriber_client.js",
  " callback\n"
  " );\n"
  " };\n"
  + " this.getSubscriberStub = function() {\n"
  + " return subscriberStub;\n"
  + " };\n"
  "\g<0>")
  # Update path discovery due to build/ dir and TypeScript conversion.
  