feat(vector-io): add OpenGauss vector database provider

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
- Implement connection and query management with psycopg2
- Provide configuration template for easy setup
- Add comprehensive unit tests

The implementation allows Llama Stack users to leverage OpenGauss as an
enterprise-grade vector database for RAG applications. Users can configure
their environment through a simple YAML configuration and environment variables.

llama_stack/templates/opengauss-demo/__init__.py

@@ -0,0 +1,9 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+# from .mymilvus_demo import get_distribution_template
+
+# __all__ = ["get_distribution_template"]