Use ChatGenerator instead of Generator

[julian-risch]

We should make the example in cookbook recipes work with ChatPromptBuilder and ChatGenerator instead of Generator as we want to shift to ChatGenerators. Or consider taking outdated recipes offline.

I searched for OpenAIGenerator with this query but there might be other Generators too.

• apify_haystack_rag_web_browser.ipynb
• newsletter-agent.ipynb
• openapitool.ipynb
• using_hyde_for_improved_retrieval.ipynb
• llama3_rag.ipynb
• query-expansion.ipynb
• query_decomposition.ipynb
• apify_haystack_rag.ipynb
• astradb_haystack_integration.ipynb
• conversational_rag_using_memory.ipynb
• rag_eval_uptrain.ipynb
• hackernews-custom-component-rag.ipynb
• metadata_enrichment.ipynb
• extracting_metadata_filters_from_a_user_query.ipynb
• model_explorer_streaming.ipynb
• rag_eval_ragas.ipynb but this one I'd say is expected to use Generator currently
• apify_haystack_instagram_comments_analysis.ipynb
• chat_with_SQL_3_ways.ipynb There is a subissue for this one "Chat With Your SQL Database" should use OpenAIChatGenerator instead of OpenAIGenerator #212