public GrpcClientBuilder clientStubFactory(GrpcClientStubFactory clientStubFactory) {
        requireNonNull(clientStubFactory, "clientStubFactory");
        return option(GRPC_CLIENT_STUB_FACTORY.newValue(clientStubFactory));
    }
Sets the {@link GrpcClientStubFactory} that creates a gRPC client stub.
If not specified, Armeria provides built-in factories for the following gRPC client stubs:
<ul>
  <li><a href="https://github.com/grpc/grpc-java">gRPC-Java</a></li>
  <li><a href="https://github.com/salesforce/reactive-grpc">Reactive-gRPC</a></li>
  <li><a href="https://github.com/grpc/grpc-kotlin">gRPC-Kotlin</a></li>
  <li><a href="https://scalapb.github.io/">ScalaPB</a></li>
</ul>
grpc/src/main/java/com/linecorp/armeria/client/grpc/GrpcClientBuilder.java