feat: Add NvidiaTextEmbedder, NvidiaDocumentEmbedder and co.

[shadeMe]

• fixes https://github.com/deepset-ai/haystack-private/issues/70

[davidsbatista]

I was doing a review, do you still want my comments?

[davidsbatista]

Overall seems to me a very good job, and kudos for already implementing the batch processing!

My only comment is regarding the assert in the code. I think assertions are better suited for tests or debugging proposes.

• If they are needed due to the type checker limitations, I would suggest a # type: ignore
• Otherwise, why not test the condition and raise an Exception?
• Also, asserts can be ignored by passing the -O flag to the interpreter

NOTE: this is not a blocker for me, I am just curious why you use them.