docs: Add Auto-Merging and Hierarchical Document Retrieval link (#10999)

* docs: Add Auto-Merging and Hierarchical Document Retrieval link

* add docs update to versioned docs 2.27

Author: julian-risch

docs-website/docs/optimization/advanced-rag-techniques.mdx

@@ -17,3 +17,4 @@ or check out one of our cookbooks 🧑‍🍳:
 - [Improving Retrieval by Embedding Meaningful Metadata](https://haystack.deepset.ai/cookbook/improve-retrieval-by-embedding-metadata)
 - [Query Expansion](https://haystack.deepset.ai/cookbook/query-expansion)
 - [Automated Structured Metadata Enrichment](https://haystack.deepset.ai/cookbook/metadata_enrichment)
+- [Auto-Merging and Hierarchical Document Retrieval](https://haystack.deepset.ai/cookbook/auto_merging_retriever)

docs-website/versioned_docs/version-2.27/optimization/advanced-rag-techniques.mdx

@@ -17,3 +17,4 @@ or check out one of our cookbooks 🧑‍🍳:
 - [Improving Retrieval by Embedding Meaningful Metadata](https://haystack.deepset.ai/cookbook/improve-retrieval-by-embedding-metadata)
 - [Query Expansion](https://haystack.deepset.ai/cookbook/query-expansion)
 - [Automated Structured Metadata Enrichment](https://haystack.deepset.ai/cookbook/metadata_enrichment)
+- [Auto-Merging and Hierarchical Document Retrieval](https://haystack.deepset.ai/cookbook/auto_merging_retriever)