add mobilebert onnx configs (#17029)

* update docs of length_penalty

* Revert "update docs of length_penalty"

This reverts commit 466bf4800b75ec29bd2ff75bad8e8973bd98d01c.

* add mobilebert onnx config

* address suggestions

* Update auto.mdx

* Update __init__.py

* Update features.py

tests/onnx/test_onnx_v2.py

@@ -180,6 +180,7 @@ PYTORCH_EXPORT_MODELS = {
     ("electra", "google/electra-base-generator"),
     ("roberta", "roberta-base"),
     ("roformer", "junnyu/roformer_chinese_base"),
+    ("mobilebert", "google/mobilebert-uncased"),
     ("xlm-roberta", "xlm-roberta-base"),
     ("layoutlm", "microsoft/layoutlm-base-uncased"),
     ("vit", "google/vit-base-patch16-224"),