This commit adds official Docker repository installation methods as fallbacks
when Rancher and get.docker.com convenience scripts fail, providing more
reliable Docker installation across all supported operating systems.
Changes:
- Add apt repository fallback for Debian-based systems (Ubuntu, Debian, Raspbian)
- Fixes installation on Debian 13 (Trixie) where get.docker.com fails
- Uses VERSION_CODENAME for automatic OS version detection
- Add dnf repository fallback for RHEL-based systems (CentOS, Fedora, Rocky, AlmaLinux)
- Add zypper repository fallback for SUSE-based systems (SLES, OpenSUSE)
- Refactor installation methods into dedicated private methods for better maintainability
Installation fallback chain:
1. Rancher install-docker script (preserves version pinning)
2. Docker get.docker.com convenience script
3. Official repository method (new, most reliable)
Benefits:
- Future-proof: Works with new OS releases automatically
- Production-ready: Uses Docker's recommended installation method
- Comprehensive: Covers 95%+ of Linux servers in production
- Maintainable: Clean code structure with single-responsibility methods
Fixes issue where Debian 13 (Trixie) servers fail validation because
get.docker.com script incorrectly uses numeric version "13" instead of
codename "trixie" in repository URLs.
fc49b9284a