Android notification payload in gRPC

How can I send Android notification payload using gRPC?
gRPC NotificationRequest struct has a special field `Alert` for iOS alert payload, but there is no
such field for Android.
```
message NotificationRequest {
repeated string tokens = 1;
int32 platform = 2;
string message = 3;
string title = 4;
string topic = 5;
string key = 6;
int32 badge = 7;
string category = 8;
Alert alert = 9;
string sound = 10;
bool contentAvailable = 11;
string threadID = 12;
bool mutableContent = 13;
google.protobuf.Struct data = 14;
string image = 15;
enum Priority {
Normal = 0;
High = 1;
}
Priority Priority = 16;
}

message NotificationReply {
bool success = 1;
int32 counts = 2;
}
```

Also, looking at your code I have noticed that you hardcoded `success` value in `NotificationReply` to `true`
```
return &proto.NotificationReply{
Success: true,
Counts: int32(len(notification.Tokens)),
}, nil
```
I think this might be misleading.

Start by locating the gRPC/protobuf definitions for NotificationRequest and NotificationReply, then trace the notification handler that constructs the reply. Determine how Android payload data should be represented and how success should reflect the operation; done means Android notifications can receive the intended payload and the reply reports the actual result.

Written by the indexing model from the issue text.