Build docker image in CI

[JakobMiksch]

• fixes QSA-api Docker #46
• this PR builds a docker image when a new version (according to semantic versioning) is released
• currently the image is published to GitHub container registry. However we could adapt it to publish it alternatively to DockerHub (or maybe both)
• the GH Action "docker/metadata-action" extracts multiple Docker tags and labels per release, based on semantic versioning. example v1.2.3 would create these tags:
  • latest
  • 1
  • 1.2
  • 1.2.3
• I adapted the docs, @pblottiere let me know if I should add more
• I moved the Dockerfile from "sandbox" to the root of the project to give it an more official character. The "compose" file in "sandbox" is adapted and should work as before.

[pblottiere]

Hello @JakobMiksch,

Nice, thanks a lot for your PR 👍.

this PR builds a docker image when a new version (according to semantic versioning) is released

What do you think about creating a new docker image for the main branch too?

[JakobMiksch]

Creating a docker image from the main branch would useful for testing. So +1 from my side.
We would need to decide which tags we give to these unstable/development images then. Maybe just dev, we could also add the commit hash as image tag. This gives us the possibility to switch back to older development versions.
I can implement this as well. Alternatively we can implement this in a follow-up PR as well.
What do you think, how would you imagine this?