✨ Support few-shot classification

[roma-glushko]

Just like Glide supports text-to-text, embeddings & speech unified API, let's try to bring a support for zero/few-shot classification.
Cohere supports this case explicitly. Other providers like OpenAI/Anthropic don't.

In case provider doesn't support few-shot classification, we should be able to mimic it with prompt engineering.

Reference:

• https://docs.cohere.com/reference/classify
• https://cookbook.openai.com/examples/multiclass_classification_for_transactions

[roma-glushko]

cc @mkrueger12 just looked at your old idea at different angle. It doesn't feel like a big deal now, so I have filled this epic.