[GraphRAG] FalkorDB graph rag integration

[AgentGenie]

Replaced by #111

Why are these changes needed?

This PR integrates FalkorDB. It wraps FalkorDB as a GraphQueryEngine and could be added to an AG2 agent through GraphRagCapability.

I also include a notebook example to show how to use this feature.

Related issue number

part of #68

Checks

• I've included any doc changes needed for https://ag2ai.github.io/ag2/. See https://ag2ai.github.io/ag2/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[qingyun-wu]

@AgentGenie thanks! Could you fix the code format issues?