Smaller control image based on chatwork/helmfile

Also:

- Add a .talismanrc file to ignore files beeing scanned by
  Talisman, a "tool that installs a hook to your repository
  to ensure that potential secrets or sensitive information
  do not leave the developer's workstation".
  See https://thoughtworks.github.io/talisman/
- Add .gitlab-ci.yml to build image from CI