Update embedding model providers

[prrao87]

Per discussion with @AyushExel, the embedding registry directory in the LanceDB repo has a number of outdated files that need to be deprecated/removed.

LanceDB repo changes

• Remove siglip.py from our lancedb source files
• Remove gte.py from our lancedb source files

Docs changes

• Add note in openclip docs that it can be used for SigLip embeddings, which it now supports
• Add note in the sentence-transformers page that ALL text embedding models on Hugging Face can be used