fix BLOOM ONNX config
Fixes dynamic axes for BloomOnnxConfig. After this PR https://github.com/huggingface/transformers/pull/18344, if use_past is used
* past/present keys should have the dynamic axes `{0: 'batch', 1: 'past_sequence + sequence'}`
* past/present values should have the dynamic axes `{0: 'batch', 2: 'past_sequence + sequence'}`


Should also fix failing tests for BLOOM's ONNX export.
(tested using `RUN_SLOW=1 pytest tests/onnx/test_onnx_v2.py -k "bloom" -s -x`)
cc @lewtun @ydshieh 
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