Add AG2 framework starter example

[VasiliyRad]

Add AG2 framework starter example

The AI Agents workshop (02-frameworks/) includes starters for Agno, AutoGen, CrewAI, and LangChain/LangGraph. This PR adds an AG2 starter to fill the gap.

AG2 is the community-driven fork of Microsoft AutoGen, actively maintained with a modernized API for multi-agent orchestration.

What changed

• ag2_starter.py — Three agents (pesquisador, escritor, crítico) collaborating via GroupChat with AutoPattern and Ollama, matching the same scenario as the existing AutoGen starter (renewable energy for high school students).

• requirements.txt — Added ag2, commented out pyautogen with a note explaining the namespace conflict (both packages provide the autogen import namespace and cannot coexist in the same environment).

• 02-frameworks/README.md — Added AG2 section with characteristics, execution instructions, and usage guidance.

• 04-ai-agents-for-data-engineering/README.md — Added AG2 to the module overview and technology list.

How to test

pip install "ag2[openai]>=0.11.0"
ollama pull mistral
python ag2_starter.py

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[qingyun-wu]

@lvgalvao could you help review this PR? Thanks!