add proto config for ziln loss (#547)

* upgrade zero inflated lognormal loss

Author: yangxudong

easy_rec/python/protos/loss.proto

@@ -44,9 +44,20 @@ message Loss {
     PairwiseHingeLoss pairwise_hinge_loss = 110;
     ListwiseRankLoss listwise_rank_loss = 111;
     ListwiseDistillLoss listwise_distill_loss = 112;
+    ZILNLoss ziln_loss = 113;
   }
 };
 
+message ZILNLoss {
+  optional float mu_regularization = 1 [default = 0.01];
+  optional float sigma_regularization = 2 [default = 0.01];
+  optional float max_log_clip_value = 3 [default = 20.0];
+  optional float max_sigma = 4 [default = 5.0];
+  optional bool return_log_pred_value = 5 [default = false];
+  optional float classification_weight = 6 [default = 1.0];
+  optional float regression_weight = 7 [default = 1.0];
+}
+
 message SoftmaxCrossEntropyWithNegativeMining {
   required uint32 num_negative_samples = 1;
   required float margin = 2 [default = 0];