Add basic CI/CD functionality

This MR adds a basic CD/CD pipeline, which validates the top-level pipeline.cwl workflow with an example input.

.prepare.gitlab-ci.yml

@@ -10,6 +10,7 @@ build_ci_runner_image:
     - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
     - |
       if docker pull $CI_REGISTRY_IMAGE/ci-build-runner:$CI_COMMIT_REF_SLUG; then
+        echo "Building docker image $CI_REGISTRY_IMAGE/ci-build-runner:$CI_COMMIT_REF_SLUG"
         docker build --cache-from $CI_REGISTRY_IMAGE/ci-build-runner:$CI_COMMIT_REF_SLUG --tag $CI_REGISTRY_IMAGE/ci-build-runner:$CI_COMMIT_REF_SLUG docker/ci-runner
       else
         docker pull $CI_REGISTRY_IMAGE/ci-build-runner:latest || true