langchain[patch]: Minor Fix: Enable Passing custom_headers for Authentication in GraphQL Agent/Tool (#16413)

- **Description:** 

This PR aims to enhance the `langchain` library by enabling the support
for passing `custom_headers` in the `GraphQLAPIWrapper` usage within
`langchain/agents/load_tools.py`.

While the `GraphQLAPIWrapper` from the `langchain_community` module is
inherently capable of handling `custom_headers`, its current invocation
in `load_tools.py` does not facilitate this functionality.
This limitation restricts the use of the `graphql` tool with databases
or APIs that require token-based authentication.

The absence of support for `custom_headers` in this context also leads
to a lack of error messages when attempting to interact with secured
GraphQL endpoints, making debugging and troubleshooting more
challenging.

This update modifies the `load_tools` function to correctly handle
`custom_headers`, thereby allowing secure and authenticated access to
GraphQL services requiring tokens.

Example usage after the proposed change:
```python
tools = load_tools(
    ["graphql"],
    graphql_endpoint="https://your-graphql-endpoint.com/graphql",
    custom_headers={"Authorization": f"Token {api_token}"},
)
```
  - **Issue:** None,
  - **Dependencies:** None,
  - **Twitter handle:** None

libs/langchain/langchain/agents/load_tools.py

@@ -353,9 +353,7 @@ def _get_scenexplain(**kwargs: Any) -> BaseTool:
 
 
 def _get_graphql_tool(**kwargs: Any) -> BaseTool:
-    graphql_endpoint = kwargs["graphql_endpoint"]
-    wrapper = GraphQLAPIWrapper(graphql_endpoint=graphql_endpoint)
-    return BaseGraphQLTool(graphql_wrapper=wrapper)
+    return BaseGraphQLTool(graphql_wrapper=GraphQLAPIWrapper(**kwargs))
 
 
 def _get_openweathermap(**kwargs: Any) -> BaseTool:
@@ -455,7 +453,7 @@ _EXTRA_OPTIONAL_TOOLS: Dict[str, Tuple[Callable[[KwArg(Any)], BaseTool], List[st
     ),
     "stackexchange": (_get_stackexchange, []),
     "sceneXplain": (_get_scenexplain, []),
-    "graphql": (_get_graphql_tool, ["graphql_endpoint"]),
+    "graphql": (_get_graphql_tool, ["graphql_endpoint", "custom_headers"]),
     "openweathermap-api": (_get_openweathermap, ["openweathermap_api_key"]),
     "dataforseo-api-search": (
         _get_dataforseo_api_search,