[Feature] Add GraphQL Query Tool (#4409)

# Add GraphQL Query Support

This PR introduces a GraphQL API Wrapper tool that allows LLM agents to
query GraphQL databases. The tool utilizes the httpx and gql Python
packages to interact with GraphQL APIs and provides a simple interface
for running queries with LLM agents.

@vowelparrot

---------

Co-authored-by: Dev 2049 <dev.dev2049@gmail.com>

tests/integration_tests/utilities/test_graphql.py

@@ -0,0 +1,32 @@
+import json
+
+import pytest
+import responses
+
+from langchain.utilities.graphql import GraphQLAPIWrapper
+
+TEST_ENDPOINT = "http://testserver/graphql"
+
+# Mock GraphQL response for testing
+MOCK_RESPONSE = {
+    "data": {"allUsers": [{"id": 1, "name": "Alice", "email": "alice@example.com"}]}
+}
+
+
+@pytest.fixture
+def graphql_wrapper() -> GraphQLAPIWrapper:
+    return GraphQLAPIWrapper(
+        graphql_endpoint=TEST_ENDPOINT,
+        custom_headers={"Authorization": "Bearer testtoken"},
+    )
+
+
+@responses.activate
+def test_run(graphql_wrapper: GraphQLAPIWrapper) -> None:
+    responses.add(responses.POST, TEST_ENDPOINT, json=MOCK_RESPONSE, status=200)
+
+    query = "query { allUsers { id, name, email } }"
+    result = graphql_wrapper.run(query)
+
+    expected_result = json.dumps(MOCK_RESPONSE, indent=2)
+    assert result == expected_result