Use any Sentence Transformer from HuggingFace

This release adopts sentence transformers for embedding using local open source models downloaded automatically from HuggingFace hub.

It also keeps track of recently used models and brings it all together in a much improved selector component on the frontend.

Also includes a PR from @hydrosquall that fixed a bug using truncated embeddings in the nearest neighbor search.

One minor note: for now truncating of sentence transformers isn't supported as we don't have a way to tell if the model supports it arbitrarily. We could maintain a list of matroyshka enabled models separately.