Add docker image.

.gitlab-ci.yml

@@ -55,3 +55,20 @@ push-bats:
   needs:
     - job: build-bats
       artifacts: true
+
+# docker image:
+
+build-docker:
+  extends: .container-build
+  variables:
+    CONTEXT: images/docker
+
+push-docker:
+  extends: .container-push
+  variables:
+    CONTEXT: images/docker
+    IMAGE: ci-images
+    TAG: docker
+  needs:
+    - job: build-docker
+      artifacts: true

images/.dockerignore

+*

images/Dockerfile

+FROM docker:20.10
+# hadolint ignore=DL3018
+RUN apk add --update-cache --no-cache docker-compose

images/docker/.dockerignore

+*

images/docker/Dockerfile

+FROM docker:20.10
+# hadolint ignore=DL3018
+RUN apk add --update-cache --no-cache docker-compose