Issue #3521317: Setup GitLab CI pipeline to build and publish container image

gitlab-ci.yml

+workflow:
+  rules:
+    - if: $CI_COMMIT_TAG
+    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
+
+stages:
+  - build
+
+container-image:
+  interruptible: true
+  stage: build
+  image: quay.io/buildah/stable
+  variables:
+    # Use vfs with buildah. Docker offers overlayfs as a default, but buildah
+    # cannot stack overlayfs on top of another overlayfs filesystem.
+    STORAGE_DRIVER: vfs
+    # Write all image metadata in the docker format, not the standard OCI format.
+    # Newer versions of docker can handle the OCI format, but older versions, like
+    # the one shipped with Fedora 30, cannot handle the format.
+    BUILDAH_FORMAT: docker
+    # You may need this workaround for some errors: https://stackoverflow.com/a/70438141/1233435
+    BUILDAH_ISOLATION: chroot
+  rules:
+    - when: always
+  script:
+    - echo "${DOCKER_HUB_PASSWORD}" | buildah login -u "${DOCKER_HUB_USER}" --password-stdin docker.io
+    - buildah build -t docker.io/drflaky/flaky-tests-scraper:latest .
+    - buildah push docker.io/drflaky/flaky-tests-scraper:latest