Add YAML linter check using yamllint

.gitlab-ci.yml

@@ -11,3 +11,8 @@ dockerfiles:
     - hadolint deploy/dev/Dockerfile || RET=1
     - exit $RET
   allow_failure: yes
+
+yamllint:
+  image: sdesbure/yamllint
+  script: "yamllint $(find . \\( -name '*.yml' -o -name '*.yaml' \\))"
+  allow_failure: yes