Build normal and extended versions for the registry images

This MR addresses #29 (closed), !65 (closed) and !66 (closed).

I've tested it with CI/CD in https://gitlab.com/yaegashi/hugo:

• https://gitlab.com/yaegashi/hugo/pipelines/59482623 (update as a scheduled job)
• https://gitlab.com/yaegashi/hugo/pipelines/59482792 (test as commited by update.py)
• https://gitlab.com/yaegashi/hugo/pipelines/59482795 (test and deploy as tagged 0.55.5 by update.py)
• https://gitlab.com/yaegashi/hugo/container_registry (contains the following 3 images with latest and 0.55.5 tags)
  • registry.gitlab.com/yaegashi/hugo (normal version, the same as before)
  • registry.gitlab.com/yaegashi/hugo/hugo (identical to yaegashi/hugo)
  • registry.gitlab.com/yaegashi/hugo/hugo_extended (extended version)