Add CI script to build containers

.gitlab-ci.yml

+# Taken and modified from https://docs.gitlab.com/ee/ci/docker/using_kaniko.html
+# Licensed under CC BY-SA 4.0 (see LICENSE-3RD-PARTY.md)
+image:
+  name: gcr.io/kaniko-project/executor:debug
+  entrypoint: [""]
+
+docker-build:
+  stage: build
+  before_script:
+    - mkdir -p /kaniko/.docker
+    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /kaniko/.docker/config.json
+  script:
+    - /kaniko/executor --context $CI_PROJECT_DIR --dockerfile $CI_PROJECT_DIR/Dockerfile --destination $CI_REGISTRY_IMAGE:$CI_COMMIT_TAG
+  only:
+    - master