Optimize current gitlab-ci configuration

The current .gitlab-ci.yml define image, cache and before_script globally which is deprecated.

One option is to put them under default: keyword or use a hidden job as template.

The Deps artefacts use around 96MB of disk space and kept for 30 days.

The project can run 160 or 200 pipelines per month which represents 15GB/20GB of storage.

As the artifacts are only useful only for CI jobs of the same pipeline, we should consider having shared cache instead but for now, just expires artifact quickly.