GH-Action build dockerfiles

[luechtdiode]

devops-repo: https://github.com/luechtdiode/mk8-argo/tree/mk8-128/adventscalendar-test test-instance backend https://testbackend.advents-calendar.org/ test-instance frontend https://test.advents-calendar.org/

[luechtdiode]

issues:

• backend-url is not available on browser-side
• language-files are not served, until pr #10 is merged

[luechtdiode]

now, it's up and running :-)

[MrCode97]

Great, thank you!