Extend KnowledgeGraph to accept Graph

extend the KnowledgeGraph such it can get a Graph reference instead of creating a connection.


```python
db = FalkorDB(host='localhost', port=6379)
db.select_graph("kg_name")

kg = KnowledgeGraph(
    model_config=KnowledgeGraphModelConfig.with_model(model),
    graph=graph
)
```