fix: make apt-get fully non-interactive in containers

Issue:
- apt-get prompts for config file conflicts
- Interactive prompt: 'What would you like to do about it?'
- Blocks automated container setup

Fix:
1. Export DEBIAN_FRONTEND=noninteractive at script start
2. Add -o Dpkg::Options::="--force-confold" to all apt-get install
3. Add -o Dpkg::Options::="--force-confdef" for default choices

Applied to:
- containerd installation
- Docker installation (docker-ce, containerd.io)
- OpenTofu installation

Behavior:
- --force-confold: Keep existing config files
- --force-confdef: Use default for new configs
- No interactive prompts
- Automated installation in containers

Result:
- ✅ Fully automated setup
- ✅ No user interaction required
- ✅ Works in CI/CD pipelines
- ✅ Container-friendly