model: add pretraining gin configuration

operative_config.train.gin

@@ -0,0 +1,35 @@
+# Parameters for build_optimizer:
+# ==============================================================================
+build_optimizer.postprocessor = None
+
+# Parameters for create_trainer:
+# ==============================================================================
+# None.
+
+# Parameters for EncoderScaffold:
+# ==============================================================================
+EncoderScaffold.embedding_data = None
+EncoderScaffold.feed_layer_idx = False
+EncoderScaffold.layer_idx_as_attention_seed = False
+EncoderScaffold.layer_norm_before_pooling = False
+EncoderScaffold.mask_cfg = None
+EncoderScaffold.recursive = False
+EncoderScaffold.return_all_layer_outputs = False
+
+# Parameters for get_encoder:
+# ==============================================================================
+get_encoder.embedding_network = None
+get_encoder.hidden_layers = None
+
+# Parameters for get_eval_actions:
+# ==============================================================================
+# None.
+
+# Parameters for get_train_actions:
+# ==============================================================================
+# None.
+
+# Parameters for Trainer:
+# ==============================================================================
+Trainer.train_dataset = None
+Trainer.validation_dataset = None