Add CI configuration

.gitlab-ci.yml

+variables:
+  #ICINGA_TOKEN: set_by_project_variables
+  #GITHUB_TOKEN: set_by_project_variables
+
+trigger:
+  image: registry.icinga.com/testing/icinga-snapshotter
+  tags:
+    - docker
+  script:
+    - ./config.sh
+    - icinga-snapshotter -c icinga_snapshotter.secrets.yml --noop