migrate to kanito for build

for more information, see https://docs.gitlab.com/ee/ci/docker/using_kaniko.html

.gitlab-ci.yml

 stages:
-  - build
-  - test
   - push
 
-before_script:
-  - docker info
-
-build_image:
-  tags:
-   - shell
-  stage: build
-  script:
-    - docker build -t registry.cybbh.space/courseware-as-code/courseware-builder/container .
-  only:
-    - master
-
-test_image:
-  tags:
-   - shell
-  stage: test
-  script:
-    - docker run registry.cybbh.space/courseware-as-code/courseware-builder/container /opt/course_builder/tests.sh
-  only:
-    - master
-
 push_image:
   tags:
-   - shell
+   - docker
   stage: push
+  image:
+    name: gcr.io/kaniko-project/executor:debug
+    entrypoint: [""]
   script:
-    - docker login -u "${DOCKER_LOGIN_USER}" -p "${DOCKER_LOGIN_PASS}" registry.cybbh.space
-    - docker push registry.cybbh.space/courseware-as-code/courseware-builder/container
-    - rm ~/.docker/config.json
+    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /kaniko/.docker/config.json
+    - /kaniko/executor --context $CI_PROJECT_DIR --dockerfile $CI_PROJECT_DIR/Dockerfile --destination $CI_REGISTRY_IMAGE:$CI_COMMIT_TAG
+    - rm /kaniko/.docker/config.json
   only:
     - master
-