Implement OpenGauss vector database integration for Llama Stack with the following features:
- Add OpenGaussVectorIOAdapter for vector storage and retrieval
- Support native vector similarity search operations
- Provide configuration template for easy setup
- Add comprehensive unit tests
- Align with the latest Llama Stack provider architecture, including KVStore and OpenAI Vector Store Mixin.
The implementation allows Llama Stack users to leverage OpenGauss as an
enterprise-grade vector database for RAG applications.
