Fix issue with Metaphor Search Tool throwing error on missing keys in API response (#9051)

- Description: Fixes an issue with Metaphor Search Tool throwing when
missing keys in API response.
  - Issue: #9048 
  - Tag maintainer: @hinthornw @hwchase17 
  - Twitter handle: @pelaseyed

libs/langchain/langchain/utilities/metaphor_search.py

@@ -163,10 +163,10 @@ class MetaphorSearchAPIWrapper(BaseModel):
         for result in raw_search_results:
             cleaned_results.append(
                 {
-                    "title": result["title"],
-                    "url": result["url"],
-                    "author": result["author"],
-                    "published_date": result["publishedDate"],
+                    "title": result.get("title", "Unknown Title"),
+                    "url": result.get("url", "Unknown URL"),
+                    "author": result.get("author", "Unknown Author"),
+                    "published_date": result.get("publishedDate", "Unknown Date"),
                 }
             )
         return cleaned_results