Fix GPT-J onnx conversion (#16780)
* add gptj to TOKENIZER_MAPPING_NAMES
* fix int32 to float to avoid problem in onnx
* Update src/transformers/models/gptj/modeling_gptj.py
Co-authored-by: ChainYo <t.chaigneau.tc@gmail.com>
Co-authored-by: lewtun <lewis.c.tunstall@gmail.com>