CI: build flat-manager and publish to registry

.gitlab-ci.yml

+
+# Buildah can't use 'overlay' driver when running inside docker
+variables:
+    STORAGE_DRIVER: vfs
+
+stages:
+    - build
+
+# Expects ${DOCKERIMAGE} which should be the name+tag of the registry image.
+# Expects ${DOCKERFILE} variable which should be the path to the Dockerfile.
+.build_template:
+    stage: build
+    script:
+        # For debugging
+        - echo ${CI_REGISTRY_IMAGE} / ${DOCKERFILE} / ${DOCKERIMAGE}
+        - dnf install -y buildah podman
+        - buildah login -u gitlab-ci-token -p ${CI_JOB_TOKEN} ${CI_REGISTRY}
+
+        # Newer versions of podman/buildah try to set overlayfs mount options when
+        # using the vfs driver, and this causes errors.
+        - sed -i '/^mountopt =.*/d' /etc/containers/storage.conf
+
+        - buildah bud --format=docker --pull -f ${DOCKERFILE} -t ${DOCKERIMAGE} .
+        - buildah push ${DOCKERIMAGE}
+    after_script:
+        # don't try to use systemd/journald
+        - |
+          cat >> /etc/containers/libpod.conf << END
+          cgroup_manager = "cgroupfs"
+          events_logger = "file"
+          END
+        - buildah inspect --format "{{.FromImageID}}" ${DOCKERIMAGE}
+    only:
+        - main
+        - triggers
+        - schedules
+    retry: 1
+
+build_flat_manager_docker_arm64:
+    extends: .build_template
+    image: arm64v8/fedora
+    tags:
+        - librem5:arm64
+    variables:
+        DOCKERIMAGE: ${CI_REGISTRY_IMAGE}/base
+        DOCKERFILE: Dockerfile
+
+build_flat_manager_docker:
+    extends: .build_template
+    image: fedora:latest
+    tags:
+        - librem5
+    variables:
+        DOCKERIMAGE: ${CI_REGISTRY_IMAGE}/base
+        DOCKERFILE: Dockerfile