feat: Support for ArangoDB KnowledgeGraph via [python-arangodb](https://github.com/arangodb/python-arango)
- implementation: https://github.com/langroid/langroid/tree/main/langroid/agent/special/arangodb
- tests: [test_arangodb.py](https://github.com/langroid/langroid/blob/main/tests/main/test_arangodb.py), [test_arangodb_chat_agent.py](https://github.com/langroid/langroid/blob/main/tests/main/test_arangodb_chat_agent.py)
- example: [chat-arangodb.py](https://github.com/langroid/langroid/blob/main/examples/kg-chat/chat-arangodb.py)