Add .gitlab-ci.yml file

.gitlab-ci.yml

+stages:
+  - build
+  - test
+  - deploy
+
+build-job:
+  stage: build
+  script:
+    - cmake -G Ninja -B build
+    - cmake --build build
+
+unit-test-job:
+  stage: test
+  script:
+    - cmake --build build --target test
+
+lint-test-job:
+  stage: test
+  script:
+    - echo "Linting code... This will take about 10 seconds."
+    - sleep 10
+    - echo "No lint issues found."
+
+deploy-job:
+  stage: deploy
+  environment: production
+  script:
+    - echo "Deploying application..."
+    - echo "Application successfully deployed."