Move dependency graph criterion to Level 1

For gitlab-com/gl-infra/scalability#1331

As discussed in gitlab-com/gl-infra&587 (closed), we are looking forward to move the Service exists in the dependency graph criterion of the maturity model from level 2 back to level 1. The level 1includes the "manifest" criteria, which simply requires the owner to declare simple data to the service manifests. The dependency graph criterion is about fulfilling the relations to other services. This step should be done when the owner creates a service manifest entry.

After this step, we would make the level 1 mandatory.