Fix incorrect names for usage blenderbot for causallm (#1887)

* Fix incorrect names for usage blenderbot for causallm

* fix input dynamic shapes as dummy input seq len  != 1

* apply code style

optimum/exporters/onnx/model_configs.py

@@ -600,7 +600,7 @@ def inputs_for_default_and_seq2seq_lm(self):
     def inputs_for_causal_lm(self):
         if self.use_past_in_inputs:
             common_inputs = {
-                "input_ids": {0: "batch_size"},
+                "input_ids": {0: "batch_size", 1: "sequence_length"},
                 "attention_mask": {0: "batch_size", 1: "past_sequence_length + 1"},
             }
             for i in range(self._normalized_config.decoder_num_layers):
@@ -645,7 +645,11 @@ def outputs(self) -> Dict[str, Dict[int, str]]:
             common_outputs = super(OnnxConfigWithPast, self).outputs
             if self.use_past:
                 # When exporting decoder models with use_cache=True, both the decoder without past and with past have the KV cache as an output.
-                for i in range(self._normalized_config.encoder_num_layers):
+                for i in range(
+                    self._normalized_config.encoder_num_layers
+                    if self.task != "text-generation"
+                    else self._normalized_config.decoder_num_layers
+                ):
                     common_outputs[f"present.{i}.key"] = {0: "batch_size", 2: "past_sequence_length + sequence_length"}
                     common_outputs[f"present.{i}.value"] = {
                         0: "batch_size",