Migrate smoke tests to dgoss for structured container testing

[dkd-dobberkau]

Summary

Evaluate and potentially migrate the existing smoke tests to dgoss for more structured and maintainable container testing.

Motivation

• Current smoke tests are bash scripts in the CI workflow — functional but not easily extensible
• dgoss provides a declarative YAML format for container assertions (ports, files, processes, commands)
• Better test reporting and easier to contribute new tests

Current test coverage

• PHP extensions check
• Composer version
• Nginx config validation (nginx variants)
• GraphicsMagick presence/absence (full/slim variants)

Implementation

• Install goss/dgoss in CI
• Create goss.yaml files for each variant
• Replace inline bash tests with dgoss run commands

References

• Raised in My two cents and wishes #34 (point 9)
• goss documentation