community: Google Vertex AI Search now returns the website title as part of the document metadata (#30688)

Google vertex ai search will now return the title of the found website
as part of the document metadata, if available.

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- **Description**: Vertex AI Search can be used to index websites and
then develop chatbots that use these websites to answer questions. At
present, the document metadata includes an `id` and `source` (which is
the URL). While the URL is enough to create a link, the ID is not
descriptive enough to show users. Therefore, I propose we return `title`
as well, when available (e.g., it will not be available in `.txt`
documents found during the website indexing).
- **Issue**: No bug in particular, but it would be better if this was
here.
- **Dependencies**: None
- I do not use twitter.

Format, Lint and Test seem to be all good.

libs/community/langchain_community/retrievers/google_vertex_ai_search.py

@@ -167,6 +167,8 @@ class _BaseGoogleVertexAISearchRetriever(BaseModel):
             doc_metadata = document_dict.get("struct_data", {})
             doc_metadata["id"] = document_dict["id"]
             doc_metadata["source"] = derived_struct_data.get("link", "")
+            if derived_struct_data.get("title") is not None:
+                doc_metadata["title"] = derived_struct_data.get("title")
 
             if chunk_type not in derived_struct_data:
                 continue