This PR refactors the configuration management to unify the handling of command-line arguments, environment variables, and default settings.
Key changes:
- All configuration is now consistently managed through the `DorisConfig` object.
- Command-line arguments now correctly override environment variables and default settings.
- The default server host/port is now correctly read from the configuration.
- Wrong environment variable loading in `schema_extractor.py` has been removed.
closes#37