DOC: WebResearchRetriever can work with DuckDuckGo search? 
Labels: name: auto:question, name: area: models, name: integration: chroma

### Issue with current documentation:

I've got this code: 

```python 
llm = HuggingFaceHub(repo_id="mistralai/Mistral-7B-Instruct-v0.1",
                     model_kwargs={"temperature": 0.01, "max_length": 4096, "max_new_tokens": 2048})
# Vectorstore
vectorstore = Chroma(
    embedding_function=HuggingFaceEmbeddings(
        model_name="all-MiniLM-L6-v2"), persist_directory="./chroma_db_oai"
)

search = DuckDuckGoSearchAPIWrapper(max_results=max_num_results,
                                    region="jp-ja",
                                    time="d")


user_input = "Which are the most demanded jobs for foreigner people that don't speak Japanese?"

web_research_retriever = WebResearchRetriever.from_llm(
    vectorstore=vectorstore,
    llm=llm,
    search=search)
```

but I get this error: 

```
---------------------------------------------------------------------------
ValidationError                           Traceback (most recent call last)
Cell In[44], line 15
     12 search = DuckDuckGoSearchAPIWrapper()
     13 user_input = "Which are the most demanded jobs for foreigner people that don't speak Japanese?"
---> 15 web_research_retriever = WebResearchRetriever.from_llm(
     16     vectorstore=vectorstore,
     17     llm=llm,
     18     search=search)
     20 # Run
     21 docs = web_research_retriever.get_relevant_documents(user_input)

File ~/anaconda3/envs/jobharbor/lib/python3.10/site-packages/langchain/retrievers/web_research.py:130, in WebResearchRetriever.from_llm(cls, vectorstore, llm, search, prompt, num_search_results, text_splitter)
    123 # Use chat model prompt
    124 llm_chain = LLMChain(
    125     llm=llm,
    126     prompt=prompt,
    127     output_parser=QuestionListOutputParser(),
    128 )
--> 130 return cls(
    131     vectorstore=vectorstore,
    132     llm_chain=llm_chain,
    133     search=search,
    134     num_search_results=num_search_results,
    135     text_splitter=text_splitter,
    136 )

File ~/anaconda3/envs/jobharbor/lib/python3.10/site-packages/langchain_core/load/serializable.py:97, in Serializable.__init__(self, **kwargs)
     96 def __init__(self, **kwargs: Any) -> None:
---> 97     super().__init__(**kwargs)
     98     self._lc_kwargs = kwargs

File ~/anaconda3/envs/jobharbor/lib/python3.10/site-packages/pydantic/v1/main.py:341, in BaseModel.__init__(__pydantic_self__, **data)
    339 values, fields_set, validation_error = validate_model(__pydantic_self__.__class__, data)
    340 if validation_error:
--> 341     raise validation_error
    342 try:
    343     object_setattr(__pydantic_self__, '__dict__', values)

ValidationError: 6 validation errors for WebResearchRetriever
search -> backend
  extra fields not permitted (type=value_error.extra)
search -> max_results
  extra fields not permitted (type=value_error.extra)
search -> region
  extra fields not permitted (type=value_error.extra)
search -> safesearch
  extra fields not permitted (type=value_error.extra)
search -> source
  extra fields not permitted (type=value_error.extra)
search -> time
  extra fields not permitted (type=value_error.extra)
```

I wonder if the webresearch retriever works also with non-google search engines.. 

Thank you in advance

### Idea or request for content:

_No response_