Resolve "Enable Docker Container Build in CI Pipeline"

Related issues

eCMR backend docker images have to built and pushed to the GitLab container registry. Currently, this is disabled.

Acceptance criteria

• Implemented code changes don't diverge from the related issue.
• Documentation reflects the status quo after merge.
• Only released versions of dependencies are used (i.e. no snapshot versions).
• Pipeline still works.
• GitLab issue is up-to-date.

If necessary, the following sections have been updated:

• Readme.md
• Documentation

Proposed squash commit message

Enable Docker Container Build and Push in CI Pipeline

• Add a new last step in stage "archive" in CI pipeline the build a docker container image
• As last step the image is pushed to the GitLab container registry.
• Add a workflow rule to run a pipeline for changes in the main branche.

Closes #54 (closed)