[Feat] Add XDG Base Directory Specification support for .fsignore files

[chlorine3545]

Hello Cling development team,

I'd like to suggest improving Cling's configuration file management by adopting the XDG Base Directory Specification.

Currently, configuration files such as .fsignore are stored directly in the user's home directory. To align with modern CLI tool practices and improve file organization, it would be great if Cling could store its configuration files in $XDG_CONFIG_HOME/cling/ (defaulting to ~/.config/cling/ if the environment variable is not set).

For backward compatibility, Cling could continue to check the current home directory location if the XDG path does not exist.

Thank you for considering this suggestion, and keep up the great work!