feat: add bfloat16

[phuhung273]

Relates triton-inference-server/server#7853

Update https://github.com/triton-inference-server/server/blob/main/docs/user_guide/model_configuration.md#datatypes after this is done

[whoisj]

Thank you for your contribution!

This seems almost too easy. Can be as easy as just recognizing the data type? I would assume that there would be internals which need to be made aware/capable of handling the new data type. Maybe not.

Adding @tanmayv25 and @yinggeh to review/comment.

[whoisj]

@phuhung273 please read the Triton Contributors Contribution License Agreement. We'll need this completed prior to accepting any changes from you unless you're acting on behalf of your employer and your employer has a CCLA on file with us.

Thank you.

[MatthieuToulemont]

This PR is a lifesaver, especially given that ONNX does not support BF16 in Triton. Torchscript and ONNX are kinda the only backend that can run complex if / else logic