Allow proxy admins to add arbitrary metadata fields to MCP servers
in config.yaml under mcp_servers.<server>.mcp_info, similar to how
model_info already works.
Changes:
- Changed MCPInfo from TypedDict to Dict[str, Any] for flexibility
- Updated load_servers_from_config to preserve all custom fields
- Updated add_update_server to handle arbitrary fields from database
- Added comprehensive unit tests covering all scenarios
