add CI pipeline to build and push the Docker container

.gitlab-ci.yml

+stages:
+  - build
+
+build-job:
+  stage: build
+  image:
+    name: gcr.io/kaniko-project/executor:debug
+    entrypoint: [""]
+  script:
+    - /kaniko/executor
+      --context "${CI_PROJECT_DIR}"
+      --dockerfile "${CI_PROJECT_DIR}/Dockerfile"
+      --destination "${CI_REGISTRY_IMAGE}:latest"