message/prompt handler

[K-Schubert]

Description

Dynamically set prompt for clientLLM and retrievers.

Implement MessageBuilder class in rag.messages which builds RAG prompts and Retriever LLM prompts.

clientLLM

• In RAGProcessor, the process methods receives a MessageBuilder instance as arg. Runs the build_chat_prompt method. Retrievers
• QueryRewritingRetriever receives a MessageBuilder instance as arg. Runs the build_query_rewriting_prompt method.
• ContextualCompressionRetriever receives a MessageBuilder instance as arg. Runs the build_contextual_compression_prompt method.