Refine Weaviate docs and add RAG example (#13057)
- **Description:** Refine Weaviate tutorial and add an example for
Retrieval-Augmented Generation (RAG)
- **Issue:** (not applicable),
- **Dependencies:** none
- **Tag maintainer:** @baskaryan <!--
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- **Twitter handle:** @helloiamleonie
Co-authored-by: Leonie <leonie@Leonies-MBP-2.fritz.box>
