Hierarchical Agentic RAG example

[minmin-intel]

Description

Add an example of hierarchical multi-agent system to improve RAG performance

Issues

List the issue or RFC link this PR is working on. If there is no such link, please mark it as n/a.

Type of change

List the type of change like below. Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds new functionality)

Dependencies

1. https://github.com/opea-project/GenAIComps/pull/480

2. OpenAI model access

Tests

Tested locally with the script in tests/ folder and passed tests.

[minmin-intel]

@XuhuiRen I have updated the example name to AgentQnA and also updated readme.

[minmin-intel]

UT test_agentqna.sh with OpenAI GPT-4o-mini passed. See screenshots below. @chensuyue