Provide write_raw_* and append_raw_* aliases

The family of write_* and append_* aliases relies on cat + heredoc.

This merge request adds write_raw_* and append_raw_* aliases to disable $ expansion during the cat.

This allows, for example, to create small wrapper scripts without escaping all $.

If required, I may modify existing recipes to use the raw aliases where suitable. So far, I only identified steps/bootstrap/start_systemd_container.yaml as relevant.