Improve CI configuration

Summary

1. There will be less load on CI runners because less CI pipelines/jobs are run. Pipelines are only created for dev branches once a MR exists. Furthermore, pipelines are cancelled once a new pipeline is created for the same branch.
2. Changed naming of Docker tags to clearly separate dev from production tags. Previously, this could be confusing because dev branches generated by GitLab start with a number which leads to the same naming scheme as image tags for release variants (1-my-topic-branch vs 1-some-image-variant).

Details

• Make CI jobs interruptible

• Use default stages for CI jobs

• Simplify CI handling for building Docker images

  A single job with rules is now used instead of two jobs with YAML templating.

  Futhermore, Docker tag naming convertions were changed:

  • next for the default branch
  • dev- is added as prefix for development branches

• Run CI pipelines conditionally

  Run pipelines only for:

  • merge requests
  • the default branch
  • release branches/tags