[FEATURE REQUEST] Configurable Embedding for Knowledge Base

Is your feature request related to a problem? Please describe. Currently, Knowledge Base only supports OpenAI for embeddings, requiring external API calls. This prevents fully offline/private RAG workflows, despite Sim already supporting local LLMs via Ollama.

Describe the solution you'd like Add embedding provider selection to Knowledge Base settings (similar to LLM provider selection): OpenAI (current default) Ollama (nomic-embed-text, mxbai-embed-large, etc.)

Describe alternatives you've considered Adding custom function blocks to the workflow: It requires coding Current OpenAI works but prevents offline/private deployments

Additional context Follows existing architecture pattern (Ollama/vLLM already supported for LLMs) where users bring their own models (like current Ollama setup) Enables 100% offline RAG (local LLM + local embeddings) Privacy-conscious users/enterprises need this for compliance