Add support for loading ClickHouse Client configuration

Why it matters

This feature improves configuration management by aligning with the XDG Base Directory Specification, allowing users to store ClickHouse Client config files in standard locations. It resolves issues related to legacy configuration path limitations and enhances consistency across Linux environments.

How to use it

Place your ClickHouse Client configuration file in the XDG config directory, typically at ~/.config/clickhouse/config.xml. The client will automatically load configuration from this location in addition to the legacy directory without any extra setup.