fix: Initialize DB on stable track

In gitlab-org/gitlab#30465 (closed) we found that non-stable releasese, e.g. canary and incremental rollouts, were not working as intended when DB_INITIALIZE was set.

This was due to helm upgrade "failing" if no resources will be created, see https://github.com/helm/helm/issues/4670. This affected us because in the DB_INITIALIZE case, we do not create any deployments nor do we activate any services.

The solution proposed in this commit is to always run the database initialization step on the stable track, with services and postgres configured accordingly. The fact that initializeCommand is set should be enough to prevent deployments (this is how the chart works) but for additional safety we set replicas to 0.