Make GitLab CI run decomposed only or decomposed by default

Since !78182 (merged) we are now running CI decomposed pipeline with 2 databases. This pipeline is still optional and requires ~"pipeline:run-decomposed" to run but we should make it run on all pipelines to avoid regressions and we should probably even go further and not even bother running the non-decomposed pipeline anymore as we assume that if GitLab works with 2 databases it will work with 1.

I'm open to explore whether or not we need to run both but at the least we want decomposed to be run by default so we catch issues earlier and running both always is expensive.