ci: enable continuous integration in repo

.gitlab-ci.yml

+build-job:
+  stage: build
+  script:
+    - echo "Hello, $GITLAB_USER_LOGIN!"
+
+test-job1:
+  stage: test
+  script:
+    - echo "This job tests something"
+
+test-job2:
+  stage: test
+  script:
+    - echo "This job tests something, but takes more time than test-job1."
+    - echo "After the echo commands complete, it runs the sleep command for 20 seconds"
+    - echo "which simulates a test that runs 20 seconds longer than test-job1"
+    - sleep 20