Add support for JinaAI Re-rankers

[alvarobartt]

What does this PR do?

This PR adds the JinaBertClassificationHead in order to support the JinaBERT re-ranking models as e.g. jinaai/jina-reranker-v1-turbo-en. Note that JinaBERT's classification head is exactly the same as standard BERT's.

Warning

This PR is not yet ready to be merged, as there seem to be some discrepancies between the Sentence Transformers and ONNX outputs (those are aligned), but the outputs for the default Candle backend is not, meaning that there may be something off somewhere. Also it has yet only been tested on CPU and MPS devices, CUDA support is still missing / pending.

Fixes #579

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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