propagate "attention_mask" dtype for "use_past" in OnnxConfig.generate_dummy_inputs
Author: arampacha
Pull request: yes

# What does this PR do?

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Fixes #16538 

The `mask_dtype` is propagated to `torch.ones()` producing "attention_mask" for `past_key_values` in `generate_dummy_inputs` call. This ensures the input datatype expected by ONNX model matches default "attention_mask" `dtype`.
The fix is applied for configs where the pattern was used.

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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- [ ] Did you write any new necessary tests?

The existing tests use `*OnnxConfig.generate_dummy_inputs` method to produce inputs passed to `session.run(...)` for testing. For this reason the issue was not reported at testing - the same inputs are used for export and testing. I'm not sure if specific tests for inputs datatype is required.

Here is a [notebook](https://colab.research.google.com/gist/arampacha/b123a1350223665201d3a3c6056cf490/hf_onnx_inference.ipynb) for verifying the fix works as expected.

## Who can review?

@lewtun 

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