Replace direct CREATE EXTENSION commands with conditional checks to avoid
permission errors on Azure PostgreSQL Flexible Server where only
azure_pg_admin members can create extensions.
- Check pg_extension table before attempting to create vector extension
- Apply same fix to pgcrypto extension for consistency
- Allows following least privilege principle for database users
Fixes#12453
- Created `VectorDBBase` as an abstract base class to standardize vector database operations.
- Added required methods for common vector database operations: `has_collection`, `delete_collection`, `insert`, `upsert`, `search`, `query`, `get`, `delete`, `reset`.
- The base class can now be extended by any vector database implementation (e.g., Qdrant, Pinecone) to ensure a consistent API across different database systems.
