Fix hardcoded vars in base-os-embedded playbook. Thanks GitLab Duo Agentic Chat

This change makes the software installation process more flexible by replacing fixed version numbers with configurable variables. Instead of hardcoding specific versions (like 1.5.0) for three different Raspberry Pi Pico development tools, the system now uses placeholder variables that can be set elsewhere, allowing users to easily specify which versions they want to install without modifying the main installation script.