[ray client] ray wait() implementation (#12072)

src/ray/protobuf/ray_client.proto

@@ -56,12 +56,25 @@ message GetResponse {
   bool valid = 1;
   bytes data = 2;
 }
+message WaitRequest {
+  repeated bytes object_refs = 1;
+  int64 num_returns = 2;
+  double timeout = 3;
+}
+
+message WaitResponse {
+  bool valid = 1;
+  repeated bytes ready_object_ids = 2;
+  repeated bytes remaining_object_ids = 3;
+}
 
 service RayletDriver {
   rpc GetObject(GetRequest) returns (GetResponse) {
   }
   rpc PutObject(PutRequest) returns (PutResponse) {
   }
+  rpc WaitObject(WaitRequest) returns (WaitResponse) {
+  }
   rpc Schedule(ClientTask) returns (ClientTaskTicket) {
   }
 }