OperatorServiceStubsOptions.validateAndBuildWithDefaults not carrying over grpcMetadataProvider from WorkflowService

[tsurdilo]

If in WorkflowService we define grpcMetadataProvider

WorkflowServiceStubsOptions options = WorkflowServiceStubsOptions.newBuilder()
    .setTarget(serverAddress)
    .addGrpcMetadataProvider(new AuthorizationGrpcMetadataProvider(tokenSupplier))
    .build();
var service = WorkflowServiceStubs.newServiceStubs(options);

Then create operator service via typcal

  OperatorServiceStubsOptions operatorServiceStubsOptions =
      OperatorServiceStubsOptions.newBuilder()
          .setChannel(service.getRawChannel())
          .validateAndBuildWithDefaults();
  var operatorStub = OperatorServiceStubs.newServiceStubs(operatorServiceStubsOptions).blockingStub();

created operator service does not carry over grpc metadata from service used
user has to explicitly set again:

    OperatorServiceStubsOptions operatorServiceStubsOptions =
      OperatorServiceStubsOptions.newBuilder()
          .setChannel(service.getRawChannel())
          .addGrpcMetadataProvider(new AuthorizationGrpcMetadataProvider(tokenSupplier))
          .validateAndBuildWithDefaults();

request is to carry over this info in ServiceStubOptions.validateAndBuildWithDefaults if possible.

[maciejdudko]

Implementing this would require somehow preserving some of the interceptors on the channel while removing others, both before and after GrpcMetadata. It would be difficult to achieve with our current architecture, and considering the current solution of passing the same metadata provider to both service builders is simple enough, we don't plan to add this feature.