add gitlab-ci with phpunit, phpcs and docker build and push

.gitlab-ci.yml

+stages:
+  - test
+  - build
+
+## Cache composer packages between all jobs and all branches
+## of this project...
+cache:
+  key: one-key-to-rull-them-all
+  paths:
+    - composer-cache/
+
+before_script:
+  - cp env.gitlab-ci .env
+  - touch storage/app/db.sqlite
+  - COMPOSER_CACHE_DIR=composer-cache composer install
+  - php artisan key:generate
+  - php artisan migrate
+
+# Test with PHP7.4
+test:php74:
+  image: cylab/php74
+  stage: test
+  script:
+    - vendor/bin/phpunit --coverage-text --colors=never --coverage-html build/coverage
+    - vendor/bin/phpcs
+  artifacts:
+    paths:
+    - build/
+    expire_in: 1 month
+
+build:
+  image: docker:19.03.1
+  stage: build
+  tags:
+    - dind
+  services:
+    - docker:19.03.1-dind
+  variables:
+    DOCKER_TLS_CERTDIR: "/certs"
+  before_script:
+    - docker info
+  script:
+    - docker build -t cylab/ctf .
+
+
+build:tagged:
+  only:
+    - tags
+  image: docker:19.03.1
+  stage: build
+  tags:
+    - dind
+  services:
+    - docker:19.03.1-dind
+  variables:
+    DOCKER_TLS_CERTDIR: "/certs"
+  before_script:
+    - docker info
+  script:
+    - docker build -t cylab/ctf:$CI_COMMIT_TAG .
+    - docker tag cylab/ctf:$CI_COMMIT_TAG cylab/ctf:latest
+    - docker login -u $DOCKER_USERNAME -p $DOCKER_PASSWORD
+    - docker push cylab/ctf:$CI_COMMIT_TAG
+    - docker push cylab/ctf:latest