Pass on model_kwargs when exporting a SentenceTransformers model

[sjrl]

What does this PR do?

Fixes #2115

This passes on the model_kwargs in get_model_from_task to the SentenceTransformer's model_kwargs parameter. Additionally, we add torch_dtype to model_kwargs before doing this so we can export SentenceTransformer's models in different dtypes.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Who can review?

Tagging @michaelbenayoun for a review

[HuggingFaceDocBuilderDev]

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[echarlaix]

Thanks for the fix @sjrl !