common: add system-level config file (#26118)
* common: Add CLI > ENV > models-presets > INI precedence
1. CLI flags have the highest precedence
2. ENV vars have the second-highest precedence
3. System and User configs have the lowest precedence
- Linux/BSD/Mac
- /etc/llama.cpp/config.ini < ${XDG_CONFIG_HOME:-~/.config}/llama.cpp/config.ini
- Windows
- %PROGRAMDATA%\llama.cpp\config.ini < %APPDATA%\llama.cpp\config.ini
* fix UB
* use common_get_env
* ignore_unknown_keys
* nits
* add docs
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Co-authored-by: Xuan Son Nguyen <son@huggingface.co>
